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Journal of Colloid And Interface Science (v.368, #1)
Cover 1 (OFC).
Microwrinkles: Shape-tunability and applications by Takuya Ohzono; Hirosato Monobe (1-8).
Display Omitted► Shape-tunable microwrinkles. ► Microstructures with controllable striped undulations. ► Liquids are constrained to the microwrinkle grooves. ► Nematic liquid crystals can be aligned in the microwrinkles.Recently, spontaneously formed microwrinkle patterns on hard coating-capped elastomer surfaces have attracted the attention of both the scientific and applied research communities, because of their simple fabrication process and practical potential in diverse applications. The periodicity and statistical orientation of the microwrinkle stripes can be controlled by applying uniaxial or isotropic compressive strain. Thus, microwrinkles have been applied to cell patterning, optical gratings, pattern templates for further patterning, surfaces with anisotropic wetting properties, surfaces with unique adhesion properties, and metrology of ultrathin film properties. Our group has focused on tuning the structure of microwrinkles by exerting additional strain. This is almost impossible for micropatterns fabricated on a hard Si wafer; therefore, our technique is based on a soft substrate and the non-linear response of the system to external strain. The dynamic shape-tunability of the micropatterns shows potential for new applications, in which switching states of a system could be induced by a change in the physical boundary conditions, namely, the shape of microwrinkles.This feature article summarizes our laboratory's recent work on controlling the stripe pattern of microwrinkles and the application of shape-tunable microwrinkles to liquid manipulation and liquid crystal alignment. For liquid manipulation, the microgrooves of the microwrinkles are used as an open channel capillary, in which the tunable groove depth controls the capillary action of the liquid in the grooves. Further changes in the direction of the microgrooves, which are filled with liquid, can induce the division of the liquids into small droplets. Such methods for shaping liquids are made possible by only macroscopic control of the strain applied to the sample. The alignment of a nematic liquid crystal was also investigated. Nematic liquid crystals can be aligned by anisotropic microgrooves; therefore, we have demonstrated that microwrinkles can be used for this purpose. In addition, because microwrinkles are shape-tunable, the liquid crystal alignment could be repeatedly switched.Our research demonstrates that shape-tunable microwrinkles provide new physical boundary conditions that can control the states of the bounded material, for example: the shape of liquid droplets and the alignment of a nematic director. We expect that many other systems that interact with the tunable boundary will lead to the discovery of new phenomena and technologies.
Keywords: Microwrinkle; Shape-tunable micropattern; Liquid patterning; Liquid manipulation; Microfluidics; Stripe pattern;
Formation of a polymer particle monolayer by continuous self-assembly from a colloidal solution by Soohyun Kim; Hee-Dok Choi; Il-Doo Kim; Jong-Chan Lee; Bum Ku Rhee; Jung Ah Lim; Jae-Min Hong (9-13).
Display Omitted► Continuous growth of polymer particles monolayers over a large area. ► Control of evaporation induced flow in a colloidal solution confined between two plates. ► Monolayer particle array template for hemispherical hollow metal oxide structures.The preparation of two-dimensional monolayers of polymer particles over a large area was demonstrated via a facile solution process. Polymer microspheres were continuously self-assembled into a close-packed monolayer from a colloidal solution confined between two plates such that the top plate was carefully dragged at a constant velocity in the direction opposite that of the monolayer growth. In situ direct observation of the particle movement during the coating process confirmed that particle transport was directed toward the contact line of the solution meniscus by evaporation-induced convective flow. Sliding of the top plate apparently effectively counterbalanced the convective flow to provide the particles with a contact line for growth of a monolayer particle array. The influence of particle concentration, sliding speed of the top plate, and surface wettability of the bottom substrate were investigated and optimized. Monolayer particle arrays were successfully demonstrated as a template for the preparation of ZnO films with ordered hollow hemispherical structures. This approach is applicable to the fabrication of ordered structures of monodispersed particles composed of various materials over large areas.
Keywords: Polymer particle monolayer; Self-assembly of particle; Colloidal solution;
Diffusion of small molecules in a chitosan/water gel determined by proton localized NMR spectroscopy by Carlos García-Aparicio; Isabel Quijada-Garrido; Leoncio Garrido (14-20).
Display Omitted► We applied proton localized NMR to study diffusion of model drugs in chitosan gels. ► Determinations have spatial and temporal resolution in a non-destructive manner. ► Diffusion of caffeine, theophylline and caprolactam in chitosan follows Fick model.Proton localized NMR spectroscopy (MRS) has been applied to study the diffusion of three small molecules, caffeine, theophylline and caprolactam, in chitosan gels with different concentration of water. This technique allows the non-destructive monitorization of diffusant concentration as a function of time and location. Concentration profiles were compared with theoretical curves based on solutions of Fick's diffusion equation for the best fitting, with the appropriate boundary conditions. The measured concentration profiles show a good agreement with the Fickian law. Values of the diffusion coefficients D ranging from 6.1 × 10−6 to 3.4 × 10−6 cm2 s−1 depending on chitosan concentration and type of diffusant molecule were determined. In addition, measurements of diffusion coefficients at equilibrium conditions with proton pulsed field gradient NMR methods supported the observed Fickian behavior and showed values of D in excellent agreement with those determined by proton MRS. All these facts demonstrate that proton MRS is an appropriate method for investigating diffusion process in complex systems, such as polymer gels.
Keywords: Chitosan; Proton localized NMR resonance; Proton pulsed field gradient NMR; Diffusion; Caffeine; Theophylline; Caprolactam;
The influence of nanoparticle architecture on latex film formation and healing properties by S. Piçarra; C.A.M. Afonso; V.B. Kurteva; A. Fedorov; J.M.G. Martinho; J.P.S. Farinha (21-33).
Display Omitted► The architecture of the nanoparticles strongly influences the film formation mechanism and its healing properties. ► Interdiffusion occurs both ways across interfaces in blend films of particles swollen with linear chains of different MWs. ► Blends of cross-linked particles and particles with linear chains undergo slow interdiffusion but form strongly healed films.We present a study of chain interdiffusion in films formed by specially architectured PBMA nanoparticles by Förster Resonance Energy Transfer –FRET. Polymer nanoparticles contained linear chains with narrower molecular weight distributions than other previous reports, allowing a more detailed study. Apparent fractions of mixing and diffusion coefficients, determined from the quantum efficiency of energy transfer, were used to characterize the interdiffusion mechanism in the different films. The resistance of the films to dissolution by a good solvent was finally correlated with the interdiffusion results, in order to get information about film healing. We concluded that whenever interdiffusion occurs between nanoparticles containing linear chains and fully cross-linked nanoparticles, healing becomes more effective in spite of showing slower interdiffusion. We also observed that particles with longer chains are more effective for film healing. Finally, we concluded that interdiffusion occurs both ways across interfaces in blends formed by particles swollen with linear chains of different molecular weights.
Keywords: Polymer nanoparticles; Interdiffusion; Healing; Coatings; Emulsion polymerization; Förster Resonance Energy Transfer, FRET; Colloid; Poly(n-butyl methacrylate), PBMA; Entanglements; Cross-links;
Modification of molecular sieves MCM-41 and SBA-15 with covalently grafted pyromellitimide and 1,4,5,8-naphthalenediimide by Fabiane Jesus Trindade; José Fernando Queiruga Rey; Sergio Brochsztain (34-40).
Display Omitted► Mesoporous silicates MCM-41 and SBA-15 were grafted with aromatic imides. ► The imides employed were pyromellitimides and 1,4,5,8-naphthalenediimides. ► The new materials presented interesting absorption and emission properties.This article describes the covalent grafting of pyromellitimide and 1,4,5,8-naphthalenediimide, which are organic semiconductors with very interesting electro-optical properties, onto the walls of mesoporous molecular sieves. The mesoporous materials MCM-41 and SBA-15 were first treated with 3-aminopropyltriethoxysilane, generating materials with a surface coverage of primary amino groups. These materials were further reacted with either pyromellitic dianhydride or 1,4,5,8-naphthalenetetracarboxylic dianhydride, generating surface-bound pyromellitimide or 1,4,5,8-naphthalenediimide, respectively. The success of the modification reactions was confirmed by elemental and thermogravimetric analyses, X-ray diffraction patterns and infrared, reflectance and fluorescence spectroscopies. The results indicated that the mesoporous structure of the new materials was preserved after the modification reactions and that the chromophores were included inside the mesoporous channels with stacked aromatic rings.
Keywords: Pyromellitimides; 1,4,5,8-naphthalenediimides; 1D stacks; Mesoporous materials; MCM-41; SBA-15;
Tailoring the structure of metal oxide nanostructures towards enhanced sensing properties for environmental applications by Mingqing Yang; Junhui He (41-48).
This article reviews recent works in our laboratory on tailoring the structure of metal oxide (WO3, TiO2, F―TiO2, and CuO) nanostructures toward enhanced sensing properties for environmental applications.Display Omitted► WO3, TiO2, and F―TiO2 were used as QCM sensing layer for detection of trace DMMP. ► Nanostructural CuO were prepared and applied on QCM resonators for sensing of HCN. ► These sensors are of particular benefits in the area of environmental applications.The present article reviews recent works in our laboratory about the sensing properties to toxic gases using nanostructured WO3, TiO2, F―TiO2, and CuO functionalized quartz crystal microbalance (QCM) sensors. WO3 and TiO2 functionalized QCM sensors have much shorter response time than those functionalized by conventional hydrogen-bond acidic branched copolymers for detection of dimethyl methylphosphonate (DMMP). F―TiO2 functionalized QCM sensors can improve the gas sensing characteristics by shortening the response time but at the price of partial irreversibility. The sensing mechanism was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Varied CuO nanostructures were synthesized by simple modulation of reaction conditions. All the as-prepared CuO was applied on QCM resonators and explored for HCN sensing. Surprisingly, responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity was very high, and the response and recovery were very fast. Comparison of the specific surface areas of CuO nanostructures showed that CuO of higher surface area is more sensitive than that of lower surface area, indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. Based on experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu2O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.
Keywords: Metal oxides; Nanostructures; Quartz crystal microbalance; Sensors; Environmental applications;
Lanthanide doping-facilitated growth of ultrasmall monodisperse Ba2LaF7 nanocrystals with excellent photoluminescence by Chang-fu Xu; Mo Ma; Li-wen Yang; Song-jun Zeng; Qi-bin Yang (49-55).
Display Omitted► Monodisperse ultrasmall Ba2LnF7 (Ln = La, Ho, Er, Yb) nanocrystals were synthesized. ► Ln3+-doping acts as more than sensitizer or activator. ► Ln3+ with smaller atom radius can facilitate the growth of Ba2LaF7 nanocrystals. ► Intense upconversion emission can be observed from Ln3+-doped Ba2LaF7 nanocrystals. ► Ba2LaF7 nanocrystals present more intense upconversion than α-NaYF4.Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba2LaF7 nanocrystals with the size of sub-10 nm through a solvothermal method. We found the dopants of Ho3+, Er3+, or Yb3+ facilitated the growth of Ba2LaF7 nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF3 nanocrystals. We find that Ln3+ (e.g., Ho3+, Er3+, or Yb3+) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba2LaF7 nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln3+-doped Ba2LaF7 nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba2LaF7:Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than α-NaYF4:Yb/Er (20/1 mol%) nanocrystals under the same conditions.
Keywords: Ba2LaF7 nanocrystals; Doping; Ultrasmall; Photoluminescence;
Direct formation of iron oxide/MCM-41 nanocomposites via single or mixed n-alkyltrimethylammonium bromide surfactants by Kamal M.S. Khalil; Mai M. Khalaf; Hossnia S. Mohran; Ahmed A. Elsamahy (56-63).
Display Omitted► Mixing of surfactants improves template combustion and removal. ► Stable composites with highly dispersed Fe2O3 nanoparticles were formed. ► Specific surface area for the composite obtained with mixed surfactants > single surfactant. ► Mixing of the two surfactants tunes and improves porosity of the Fe2O3/MCM-41 composites.Iron oxide/MCM-41 nanocomposites, Fe2O3/MCM-41, containing 5%, 10%, and 20% (w/w) iron oxide, were prepared via a direct nonhydrothermal method at room temperature. The preparations were preformed by using iron(III) nitrate, tetra-ethoxysilane (TEOS), and cetyltrimethylammonium bromide (CTAB) mixed or unmixed with dodecyltrimethylammonium bromide (DTAB). The produced materials were dried and calcined at 550 °C for 3 h. Test materials were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), N2 gas adsorption/desorption isotherms, small angle and wide angle X-ray diffraction (XRD). Results indicate that mixing of CTAB with DTAB does not harm the formation of blank MCM-41 structure. For the composite Fe2O3/MCM-41 materials, results showed formation of more stable MCM-41 structure with higher surface area and improved porosity in the presence of mixed (CTAB + DTAB) than in the presence of single (CTAB) surfactants for up to 10% Fe2O3/MCM-41 (w/w). This was explained in terms of the effect DTAB on contraction of the template micellar size to compensate for the expected size expansion upon the addition of ionic iron(III) nitrate precursor. Highly dispersed Fe2O3 nanoparticles were formed in all cases even with the highest iron oxide percentage. Formation of the nanocomposites was postulated to be determined by fast nucleation and slow growth of iron oxide species, which facilitated formation of well dispersed iron oxide nanoparticles inside and on the wall of the MCM-41 material.
Keywords: Iron oxide/MCM-41; Fe2O3/MCM-41; Nanocomposite; TGA; DSC;
Surface properties of amino-functionalized poly(ε-caprolactone) membranes and the improvement of human mesenchymal stem cell behavior by Yi Zhang; Yan Zhang; Min Chen; Jinliang Yan; Zhaoyang Ye; Yan Zhou; Wensong Tan; Meidong Lang (64-69).
Display Omitted► We prepared amino-functionalized PCL with different NH2 content. ► The amino groups endowed PCL with excellent surface hydrophilicity and morphology. ► hMSCs' adhesion, proliferation, and osteogenic differentiation were promoted. ► Cell behavior was significantly mediated by surface properties.In this study, a series of membranes with different amino group densities were prepared to investigate the surface properties of the novel poly(γ-amino-ε-caprolactone-co-ε-caprolactone) (NPCL) copolymer synthesized by our laboratory. Meanwhile, the human mesenchymal stem cells' (hMSCs) behavior on those membranes was examined. The molecular characteristics of the NPCL copolymers were characterized by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). Surface properties of membranes were characterized by water contact angle analysis, X-ray photoelectron spectroscopy analysis (XPS), and atomic force microscopy (AFM). It was found that the incorporation of amino groups to the poly(ε-caprolactone) (PCL) backbone resulted in an augmented wettability, a decreased crystallinity, and also an increased surface roughness on the NPCL membranes. In vitro cell experiments showed a significant enhancement in hMSCs' adhesion, proliferation, and osteogenic differentiation on NPCL membranes compared with virgin PCL membrane, and demonstrated that surface properties of membrane played an important role in tailoring cell behavior.
Keywords: Functionalized poly(ε-caprolactone); Amino groups; Surface properties; hMSC;
Cobalt oxide silica membranes for desalination by Chun Xiang C. Lin; Li Ping Ding; Simon Smart; João C. Diniz da Costa (70-76).
.Display Omitted► CoO x Si membranes processed low (NaCl 1 wt.%) and high salinity (7.5–15 wt.%) waters. ► CoO x Si films became hydrostable after 5 days of water exposure up to 75 °C. ► Best water fluxes of 1.8 kg m−2 h−1 at 1 wt.% salt feed concentration. ► High salt rejections >99% were mainly attributed to CoO x Si molecular sieving.This work shows for the first time the potential of cobalt oxide silica (CoO x Si) membranes for desalination of brackish (1 wt.% NaCl), seawater (3.5 wt.% NaCl) and brine (7.5–15 wt.% NaCl) concentrations at feed temperatures between 25 and 75 °C. CoO x Si xerogels were synthesised via a sol–gel method including TEOS, cobalt nitrate hydrate and peroxide. Initial hydrothermal exposure (<2 days) of xerogels prepared with various pH (3–6) resulted in densification of the xerogel via condensation reactions within the silica matrix, with the xerogel synthesised at pH 5 the most resistant. Subsequent exposure was not found to significantly alter the pore structure of the xerogels, suggesting they were hydrostable and that the pore sizes remained at molecular sieving dimensions. Membranes were then synthesised using identical sol–gel conditions to the xerogel samples and testing showed that elevated feed temperatures resulted in increased water fluxes, whilst increasing the saline feed concentration resulted in decreased water fluxes. The maximum flux observed was 1.8 kg m−2 h−1 at 75 °C for a 1 wt.% NaCl feed concentration. The salt rejection was consistently in excess of 99%, independent of either the testing temperature or salt feed concentration.
Keywords: Cobalt oxide silica membranes; Hydrostability; Molecular sieving; Water flux; Salt rejection;
Correlation between catalytic activity and surface ligands of monolayer protected gold nanoparticles by Mrinmoy Biswas; Enakshi Dinda; Md. Harunar Rashid; Tarun K. Mandal (77-85).
Display Omitted► Different ligand-capped Au NPs' thin films and Au NPs' suspensions are synthesized. ► Capping-ligand effect on the catalytic activities of Au NPs' thin films are studied. ► Capping-ligand effect on the catalytic activities of Au NPs' suspension are studied. ► Reduction of nitrophenol and ferricyanide–thiosulfate redox reaction are studied. ► Some ligands completely destroy the catalytic activity of Au NPs.Gold nanoparticles (GNPs) are known to be a very good catalyst. Also, the anchoring of GNPs with stabilizing ligands is essential for surface modification, tuning of size and shapes, and to prevent from aggregation in suspension. But the effect of ligand on the catalytic property of ligand-capped GNP is yet to be explored in detail. In this paper, we perform an in-depth study of effect of ligands on the catalytic activity of monolayer protected GNPs. For this study, a series of different ligand functionalized GNPs in suspension as well as functionalized GNPs' thin film on glass substrate are prepared and used as catalysts in two model reactions, viz. borohydride reduction of 4-nitrophenol and redox reaction between potassium ferricyanide and sodium thiosulfate. The functionalization of GNPs with any ligand reduces its virgin catalytic activity, no matter whether the GNPs are suspended or supported as thin film. An increase in alkyl chain length of alkanethiols and alkylamines ligands and their graft density to the surface of GNP reduces its catalytic activity. Interestingly, the capping of GNPs with 11-mercaptoundecanoic acid and 11-mercaptoundecanol ligands completely destroys its catalytic activity. The effect of anchoring group of ligand molecules on the catalytic activity of ligand-protected GNPs is also discussed.
Keywords: Gold nanoparticles; Thin film; Catalysts; Ligand-capped; 4-Nitrophenol;
Hydrodynamic and interparticle potential effects on aggregation of colloidal particles by X.J. Cao; H.Z. Cummins; J.F. Morris (86-96).
Display Omitted► Colloidal particles aggregate into networks percolating at lower volume fraction. ► Repulsive barrier of energy affects the microstructure of particle networks. ► Hydrodynamic interactions have an impact on particle aggregation process. ► Hydrodynamics slows the evolution of linear-like three-particle groups.The effects of both hydrodynamic interaction and the form of the interparticle potential on the aggregation process for dispersed spherical particles are investigated by computational simulation. The simulation methods of Brownian Dynamics (BD) and Stokesian Dynamics (SD) are applied, over a range of solid volume fraction of 0.04 ⩽ ϕ ⩽ 0.12 . The interparticle potential is a combination of a generalized Lennard-Jones form and a Yukawa potential, the latter of which describes a screened electrostatic repulsion at longer range. The combined potential is parameterized to include a roughly constant primary minimum near contact, along with a variable repulsive barrier at slightly larger separation. The microstructure is characterized through the pair distribution function, g(r), and the static structure factor. The repulsive barrier reduces the rate of aggregation and is also seen to affect the structure, with a large repulsion associated with a more tenuous structure. This is reflected in the potential having a strong effect on the evolution of 'bonds' per particle. Hydrodynamic interactions were found to reduce the solid fraction required for percolation, with the influence depending upon the form of the potential; the difference in percolation threshold was significant, with ϕ c , SD ≐ 0.06 and ϕ c , BD ⩾ 0.08 a typical difference for moderate repulsion barriers. These results are for 864 particles in a cubic unit cell. To address the mechanism for this influence of hydrodynamic interactions, a complementary analysis of the evolution of numerous independent three-particle aggregates was performed. The analysis shows that hydrodynamic interaction slows the evolution toward a condensed aggregate of lowest potential energy in a way which cannot be explained by a simple rescaling of the drag due to uncorrelated particle motions.
Keywords: Aggregation; Hydrodynamic force; Simulation; Repulsive force; Percolation; Structure evolution;
Facile organic solvent-free synthesis of size-controlled hierarchically structured magnetic hollow spheres and potential application in adsorption for bovine serum album by Cong Zhang; Hui Zhang; Bing Du; Rong Hou; Shaohuan Guo (97-106).
Display Omitted► Organic solvent-free synthesis of size-controlled magnetic hollow spheres(MHS). ► Polystyrene template curvature – effect on the morphology of MHS. ► MHS sphere wall is composed of primary nanoparticles with varied morphologies and stacking modes. ► MHS with nanorodlike primary particles vertically stacked wall shows the maximum BSA adsorption.A series of size-controllable hierarchically nanostructured magnetic hollow spheres (MHS) (250–2330 nm) have been fabricated by using the hard-template method involving the coprecipitation of ferrite precursor over the pre-synthesized polystyrene spheres with varied sizes under organic solvent-free conditions followed calcinations. The SEM, TEM and HRTEM results indicate that the primary nanoparticles constructing hierarchically nanostructured MHS clearly show the template sphere size-dependent changes in morphologies and stacking modes from disorderly stacked globular and nanorodlike mixed particles, to orderly perpendicularly oriented nanorodlike particles, and to compact horizontally arranged nanospindle particles as the template size is increased. The N2 adsorption–desorption data reveal that the MHS spheres have a high BET surface area (48–83 m2/g) and large pore volumes (0.37–0.66 cc/g). The vibration sample magnetization analysis shows that the MHS spheres have moderate magnetization saturation of 24–37 emu/g. The adsorption results show that the BSA adsorbance is greatly affected by the varied morphologies and stacking modes of primary nanoparticles constructing the MHS spheres and the maximum adsorption occurs on the MHS spheres mainly comprised of perpendicularly oriented nanorodlike primary particles.
Keywords: Size-controllable; Magnetic hollow spheres; Coprecipitation; Organic solvent-free; Morphology change; Ferrite; Adsorption;
Preparation of organic/inorganic hybrid and hollow particles by catalytic deposition of silica onto core/shell heterocoagulates modified with poly[2-(N,N-dimethylamino)ethyl methacrylate] by Tatsuo Taniguchi; Shun Obi; Yoshitada Kamata; Takuya Kashiwakura; Masakatsu Kasuya; Tatsuya Ogawa; Michinari Kohri; Takayuki Nakahira (107-114).
Display Omitted► Core and shell particles were prepared by dispersion and emulsifier-free emulsion polymerization. ► Heterocoagulates were fabricated by coagulation between core and shell particles. ► Surface modification was carried out by surface-initiated ATRP from heterocoagulates. ► Surface-grafted heterocoagulates were catalytically hybridized with silica. ► Hollow particles with controlled morphology were obtained by calcination of hybrids.The organic/inorganic hybrid particles PSt/P(St-CPEM) θ -g-PDMAEMA/SiO2 were prepared by catalytic hydrolysis and subsequent polycondensation of tetraethoxysilane in the poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA) layers grafted on the PSt/P(St-CPEM) θ core/shell heterocoagulates. The micron-sized PSt core and the submicron-sized P(St-CPEM) shell particles bearing ATRP initiating groups were synthesized by dispersion polymerization of styrene (St) and emulsifier-free emulsion polymerization of St with 2-chloropropionyloxyethyl methacrylate (CPEM), respectively. The raspberry-shaped PSt/P(St-CPEM) θ heterocoagulates with a controlled surface coverage (θ = 0.51, 0.81) were prepared by hydrophobic coagulation between the core and the shell particles in an aqueous NaCl solution near the T g of P(St-CPEM). Surface modification of heterocoagulates was carried out by ATRP of DMAEMA from the shell particles adsorbed on the core particles. Silica deposition was performed by simply adding tetraethoxysilane to a water/methanol dispersion of PSt/P(St-CPEM) θ -g-PDMAEMA. The SEM and TGA revealed that the resulting PSt/P(St-CPEM) θ -g-PDMAEMA/SiO2 composites maintain a raspberry-like morphology after deposition of silica onto the PDMAEMA layer grafted on heterocoagulates. The micron-sized, raspberry-shaped or the submicron-sized, hole-structured silica hollow particles were obtained selectively by thermal decomposition of the PSt/P(St-CPEM) θ -g-PDMAEMA/SiO2. The oriented particle array was fabricated by dropping anisotropically perforated silica particles onto a glass substrate settled at the bottom of a bottle filled with chloroform.
Keywords: Heterocoagulates; Atom transfer radical polymerization; Silica; Hybrid particles; Hollow particles;
Antisolvent precipitation of hydrophobic functionalized multiwall carbon nanotubes in an aqueous environment by Chintal Desai; Susana Addo Ntim; Somenath Mitra (115-120).
Display Omitted► The precipitation of organic soluble f-CNTs in aqueous media is presented. ► Highly stable dispersion in solvent/water mixtures. ► Particle aggregation increased with the addition of electrolytes. ► THF/water system showed the best long term stability in presence of electrolytes.The possibility of antisolvent precipitation of hydrophobic, organic soluble functionalized carbon nanotubes (f-CNTs), where water acts as an antisolvent is presented. Octadecylamine functionalized multiwall carbon nanotubes (MWCNT-ODA) was used as the model compound and was found to form highly stable dispersions in different water/solvent systems, and the particle sizes ranged from 170 to 400 nm. Colloidal behavior was studied using dynamic light scattering and particle aggregation was found to increase with the addition of electrolytes, with tetrahydrofuran (THF) and ethanol showing the maximum effect. The aggregation behavior of the antisolvent precipitated system did not follow the conventional Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, which was different from what has been reported previously for hydrophilic, water soluble f-CNTs. Based on this study, it is evident that hydrophobic f-CNTs are potential water pollutants.
Keywords: Stability; Dispersion; Precipitation; Carbon nanotubes; Functionalization;
Novel TiO2/C nanocomposites: Synthesis, characterization, and application as a photocatalyst for the degradation of organic pollutants by Elias da Costa; Patricio P. Zamora; Aldo J.G. Zarbin (121-127).
Display Omitted► Novel TiO2/carbon nanocomposites prepared and characterized. ► Photocatalysts for degradation of organic dyes in aqueous solution. ► Excellent photocatalytic performance. ► Easy separation of catalyst from the reaction.Novel TiO2/carbon nanocomposites were prepared through the pyrolysis of TiO2/poly(furfuryl alcohol) hybrid materials, which were obtained by the sol–gel method, starting from titanium tetraisopropoxide (TTIP) and furfuryl alcohol (FA) precursors. Six different TiO2/C samples were prepared based on different TiO2 nanoparticle sizes and TiO2/FA ratios. All of the samples were characterized using X-ray diffraction, infrared, and Raman spectroscopy. The results indicated effective FA polymerization onto the TiO2 (anatase) nanoparticles, polymer conversion to disordered carbon following the pyrolysis, and a simultaneous TiO2 anatase–rutile phase transition. The resulting TiO2/carbon composites were used as photocatalysts in the advanced oxidative process (AOP) for the degradation of reactive organic dyes in aqueous solution. The results indicate excellent photocatalytic performance (degradation of 99% of the dye after 60 min) with several advantages over traditional TiO2-based photocatalysts.
Keywords: Heterogeneous photocatalysis; TiO2 nanoparticles; TiO2/C nanocomposites;
Self-generated hierarchically porous titania with high surface area: Photocatalytic activity enhancement by macrochannel structure by Xiao-Yun Li; Li-Hua Chen; Yu Li; Joanna Claire Rooke; Chao Wang; Yi Lu; Alain Krief; Xiao-Yu Yang; Bao-Lian Su (128-138).
Various hierarchical porous titania with very high surface area over 600 m2/g have been synthesized via a spontaneously self-formation process from organic titanium alkoxides by a water adjusting approach using acetonitrile as reaction medium. The effect of porous structure on the photocatalytic activity of dye molecules degradation reaction has been studied.Display Omitted► Hierarchically porous titania materials. ► Self-formation process from titanium alkoxides. ► Very high surface area of 600 m2/g. ► Acetonitrile as reaction medium. ► Photocatalytic activity enhancement.Various hierarchical porous titania with high surface area over 600 m2/g have been synthesized via a spontaneous self-formation process from titanium alkoxides by a water adjusting approach using acetonitrile as reaction medium. The reactivity of metal alkoxides and the water content in acetonitrile medium on the resultant structure have been investigated. The porosities of the products were characterized by SEM, TEM and N2 adsorption–desorption measurements. The observation on the evolution of porous structure with increasing water content in reaction system is essential for a better understanding of hierarchical porous structure formation over different length scales by this self-formation process. The creation of macro/micropores in photocatalytic titania materials has been found to enhance the photocatalytic activity due to both the action of macrochannels as light harvester and the easy diffusion effect of organic molecules. The present work shows clearly that hierarchically porous titania with the presence of macroporous structure and high surface area can be very efficient photocatalysts, suggesting their potential applications in water treatment as decontamination materials.
Keywords: Micro–macroporous; Porous titania; Metal alkoxides; Spontaneous self-formation; Acetonitrile medium; Photocatalytic activity;
Preparation of thermally stable well-dispersed water-soluble CdTe quantum dots in montmorillonite clay host media by Yuan-Cheng Cao (139-143).
Display Omitted► Water soluble CdTe QDs was well dispersed in montmorillonite clay to produce QDs/clay powder using frozen dryer. ► CdTe QDs dispersed in the clay particles duo to the charge. ► The QDs/clay powder can be dispersed in water without changing the fluorescent property. ► QDs/clay powder was used to prepare the fluorescent thin film by extrusion without sacrificing the optical property.In this work, a method to prepare a thermally stable QDs/clay powder is reported. First, several water soluble CdTe QDs characterised by different size-dependent emission wavelengths were synthesised through wet chemistry. Montmorillonite-Na+ clay in water was dispersed into a muddy suspension by sonication. Then, the clay-water suspension was used as the host media for CdTe QDs to prepare the QDs/clay powder by freeze drying. The experiments showed that QDs/clay powder could be re-dispersed in water without changing the luminescent property of the QDs; this process was reversible. EDX showed that Cd and Te elements existed in the QDs/clay powder and the XRD tests showed that the clay [0 0 1] reflection peaks for raw clay, QDs (λ em = 514 nm)/clay and QDs (λ em = 560 nm)/clay were the same, namely 2θ = 7.4°. Finally, QDs/clay powder was applied to the HDPE polymer extrusion process at 200 °C to produce thin films; the resultant QDs-polymer nanocomposite film exhibited strong fluorescence.
Keywords: Quantum dots; Layered materials; Clay; Luminescent film; Polymer nanocomposites;
Gold nanoparticles generated and stabilized by water soluble curcumin–polymer conjugate: Blood compatibility evaluation and targeted drug delivery onto cancer cells by S. Manju; K. Sreenivasan (144-151).
Display Omitted► Curcumin conjugated AuNPs were synthesized using hyaluronic acid-curcumin conjugates. ► HA–Cur@AuNPs were further HA–Cur@AuNPs modified with folate conjugated PEG to improve the cancer cell targeting. ► PF.HA–Cur@AuNPs exhibited better dose dependent cytotoxicity toward different cancer cell lines. ► PF.HA–Cur@AuNPs demonstrated enhanced targeting efficacy of 95.4%.Curcumin (Cur) shows low anticancer activity in vivo due to its reduced systemic bioavailability stemmed from its poor aqueous solubility and instability. Suitably functionalized nanocarriers designed to empty the drug specifically at tumor sites can potentially enhance the antitumor activity of Cur. We devised a simple method for the fabrication of water soluble Cur conjugated gold nanoparticles to target various cancer cell lines. Cur was conjugated to hyaluronic acid (HA) to get a water soluble conjugate (HA–Cur). We generated gold nanoparticles (AuNPs) by reducing chloroauric acid using HA–Cur, which played the dual role of a reducing and stabilizing agent and subsequently anchored folate conjugated PEG. These entities were probed using different analytical techniques, assayed the blood compatibility and cytotoxicity. Their interaction with cancer cell lines (HeLa cells, glyoma cells and Caco 2 cells) was followed by flow cytometry and confocal microscopy. Blood–materials interactions studies showed that the nanoparticles are highly hemocompatible. Flow cytometry and confocal microscopy results showed significant cellular uptake and internalization of the particles by cells. HA–Cur@AuNPs exhibited more cytotoxicity comparing to free Cur. The strategy, we adopted here, resulted the formation blood compatible Cur conjugated AuNPs with enhanced targeting and improved efficacy.
Keywords: Gold nanoparticle; Hyaluronic acid; Water soluble curcumin; Folic acid conjugated polyethylene glycol; Hemocompatibility;
Tuning mechanical properties of liquid crystalline nanoparticles by Jing C. Zhou; Stanislav Tsoi; Christopher M. Spillmann; Jawad Naciri; Banahalli Ratna (152-157).
Display Omitted► Synthesis of colloidal nanoparticles composed of a gel-like network. ► Mechanical analysis of the nanoparticles using nanoscale indentation. ► Tuning stiffness of the nanoparticles by changing network structure. ► A model to explain the polymer network effect on mechanical properties.We report the synthesis of colloidal nanoparticles with an internal structure forming a gel-like matrix. These nanoparticles are composed of low molecular weight liquid crystal (LC) 4-pentyl-4-cyanobiphenyl (5CB) encapsulated in an LC-based polymer network. Using nanoscopic mechanical analysis, we demonstrate the ability to independently tune the shape anisotropy and stiffness by varying, respectively, the 5CB concentration and the extent of the polymer cross-linking. Based on these data, a model is introduced to account for the effect of the polymer network on the mechanical properties, thus providing novel insight into the nanomechanics of these soft particles.
Keywords: Liquid crystalline nanoparticle; Gel-like matrix; Mechanical analysis; 5CB; Stiffness; Shape anisotropy;
Synthesis of cross-linked epoxy microparticles: Effect of the synthesis parameters by Matteo Traina; Jocelyne Galy; Jean-François Gérard; Tamara Dikic; Tom Verbrugge (158-164).
.Display Omitted► Crosslinked microparticles were synthesized via precipitation polymerization. ► Spherical microparticles based on epoxy–amine networks were obtained. ► Particle formation was related to a reaction-induced phase separation mechanism. ► Synthesis parameters (c, a/e, T) and the structure of the diamine were varied. ► These parameters affect the characteristics of the microparticles (Φ, Tg ).Epoxy crosslinked microparticles were synthesized from the reaction between diglycidyl ether of bisphenol A and a diamino hardener, through precipitation polymerization in a polypropylene glycol solvent. The influence of the monomer concentration, the amine/epoxy stoichiometric ratio, the reaction temperature and the structure of the diamine (aromatic or cycloaliphatic) were investigated, since these parameters may affect the structure and properties of the particles. Morphological analysis revealed that, in all cases, spherical particles were obtained with diameters ranging from 1 to 6 μm. The glass transition temperatures of the particles was found to vary between 130 and 160 °C using the aromatic diamine and between 116 and 141 °C using the cycloaliphatic diamine. It was also found that the effective stoichiometry of the particles was different from the initial stoichiometry in the feed solution.
Keywords: Cross-linked polymer microparticles; Precipitation polymerization; Epoxy–amine networks; Phase separation;
Facile synthesis and multicolor luminescent properties of uniform Lu2O3:Ln (Ln = Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) nanospheres by Rumin Li; Shili Gai; Liuzhen Wang; Jun Wang; Piaoping Yang (165-171).
Display Omitted► A facile precipitation method was used to prepare uniform Lu2O3:Ln nanospheres. ► The samples exhibit multicolor down-conversion and up-conversion luminescence. ► The possible formation mechanism was well investigated. ► The color of the phosphors was tuned by doping different rare earth ions.Multicolor Lu2O3:Ln (Ln = Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) nanocrystals (NCs) with uniform spherical morphology were prepared through a facile urea-assisted homogeneous precipitation method followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrum (EDS), Fourier transformed infrared (FT-IR), thermogravimetric and differential thermal analysis (TG–DTA), and photoluminescence (PL) spectra as well as kinetic decays were employed to characterize these samples. The XRD results reveal that the as-prepared nanospheres can be well indexed to cubic Lu2O3 phase with high purity. The SEM images show the obtained Lu2O3:Ln samples consist of regular nanospheres with the mean diameter of 95 nm. And the possible formation mechanism is also proposed. Upon ultraviolet (UV) excitation, Lu2O3:Ln (Ln = Eu3+ and Tb3+) NCs exhibit bright red (Eu3+, 5D0 → 7F2), and green (Tb3+, 5D4 → 7F5) down-conversion (DC) emissions. Under 980 nm NIR irradiation, Lu2O3:Ln (Ln = Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) NCs display the typical up-conversion (UC) emissions of green (Er3+, 4S3/2,2H11/2 → 4I15/2), blue (Tm3+, 1G4 → 3H6) and yellow-green (Ho3+, 5F4, 5S2 → 5I8), respectively.
Keywords: Luminescence; Lu2O3; Urea; Nanospheres; Precipitation method;
Immobilization of poly(fluorene) within clay nanocomposite: An easy way to control keto defect by Chanchal Chakraborty; Kausik Dana; Sudip Malik (172-180).
Display Omitted► Polymer–nanocomposites composed of cationic poly(fluorene) and native MMT prepared by solution blending method. ► Change of overall morphology of composites films. ► Enhanced thermal stability and photostability of composites than pristine poly(fluorene). ► Effective way to tune the keto defects.Blue light emitting cationic polyfluorene polymer(PF)/montmorillonite (MMT) nanocomposites were prepared by solution intercalation and exfoliation method to evaluate the effect of MMT on the nanocomposite structures, properties and morphologies. The properties of PF–MMT composites, containing 1–50 mass% MMT, were characterized unambiguously with the help of multiple analytical techniques, with focus on the keto defect and photostability of PF in the nanocomposites. XRD and HRTEM studies reveal both exfoliation of MMT galleries at lower content of MMT in composites and intercalation of PF chains into the MMT galleries at higher MMT content. The nanocomposites show higher thermal stability than pristine PF as anchorage of nanoclay in PF matrix occur through the electrostatic interaction between nanoclay and polymer. The decrease in Si–O–Si stretching frequency during exfoliation is much higher than in intercalation, as Si–O–Si experience lesser hindrance to vibrate in exfoliated MMT galleries. The gradual redshift of π–π* transition peak of PF with increasing MMT content in composites confirms the uncoiling of PF in clay galleries. The photoluminescence characteristics reveal interruption of interchain interaction in this intercalated and exfoliated organic/inorganic hybrid system, which reduces the low-energy emission that results from keto defect. Due to very high aspect ratio of MMT, it can act as an efficient exciton blocking layer and a barrier to oxygen diffusion, which may lead to a device with high color purity and enhanced photostability. Again current–voltage characteristics of nanocomposite films confirm the retention of LED properties after nanocomposite formation.
Keywords: Poly(fluorene); Montmorillonite; Nano-materials; Photostability; Keto-defect;
Synergistic effect of polycation and polyanion on silica polymerization by Bingru Zhang; Shaohua Xin; Yuning Chen; Fengting Li (181-190).
Display Omitted► AA/AT/DE is an efficient and environmental friendly silica scale inhibitor. ► The addition of PESA can improve the inhibitory performance of AA/AT/DE. ► White flocs formed during the inhibition process can be dissolved by PESA.Colloidal silica (SiO2) is perhaps the most undesirable inorganic deposit formed in industrial water treatment systems. SiO2 can either be found in bulk or on surfaces, such as heat exchangers, pipelines, or membrane. Conventional mineral scale inhibitors cannot inhibit its formation. Chemical cleaning is difficult and not free from hazards. This paper reports the excellent inhibition efficiency of adipic acid/amine-terminated polyethers D230/diethylenetriamine copolymer (AA/AT/DE). However, a small amount of silica-AA/AT/DE white insoluble floc appears in the solution. To overcome this problem, polyepoxysuccinic acid (PESA) is introduced. PESA by itself cannot inhibit silica polymerization. However, the combination of PESA and AA/AT/DE cannot only prevent the white floc, but also improve the inhibition performance of AA/AT/DE. The underlying mechanism is investigated based on zeta potentials and atomic force microscopy topography.
Keywords: Silica; Polymerization; Inhibition; Polymer;
Photofunctional multilayer films by assembling naked silver nanoparticles and a tailored nitric oxide photodispenser at water/air interface by Elisa Vittorino; Gabriele Giancane; Daniela Manno; Antonio Serra; Ludovico Valli; Salvatore Sortino (191-196).
Display Omitted► Nanostructured hybrid films of silver nanoparticles (AgNPs) and a tailored nitric oxide (NO) photodonor. ► Strong interactions between the two components at the air/water interface. ► Presence of both isolated AgNPs and nanoassemblies of AgNPs in the films. ► Release of NO exclusively controlled by visible light stimuli. ► Intriguing bimodal systems for biomedical research studies.This contribution reports the design, preparation, and characterization of nanostructured hybrid films of silver nanoparticles (AgNPs) and a tailored nitric oxide (NO) photodonor. They were achieved by exploiting effective interfacial interactions between an amino-terminated NO photodonor spread onto water surface and naked AgNPs dissolved in the water subphase. The morphology, the spectroscopic features, and the interaction between the two components in the floating films at the air/water interface were inspected by Brewster Angle Microscopy, UV–Vis reflection, and polarization–modulation infrared reflection–absorption spectroscopy. AgNPs and the NO photodonor were successfully transferred onto hydrophobized quartz substrates by horizontal lifting deposition and the resulting multilayer films were characterized by UV–Vis absorption spectroscopy and transmission electron microscopy, respectively. The results obtained showed the presence of both isolated AgNPs and assemblies of AgNPs having nanodimensional character in the films. The photochemical properties of the NO photodonor were well preserved in the hybrid multilayers. In fact, they were able to release NO under visible light excitation, as unambiguously demonstrated by the direct and in real-time monitoring of this transient species using an ultrasensitive electrode, and the transfer of the released NO to a protein such as myoglobin.
Keywords: Silver; Nanoparticles; Nitric oxide; Light; Films; Release;
Surface glycosylation of polysulfone membrane towards a novel complexing membrane for boron removal by Jianqiang Meng; Jing Yuan; Yinlin Kang; Yufeng Zhang; Qiyun Du (197-207).
Display Omitted► A glycopolymer was tethered onto polysulfone membrane for boron removal. ► Adsorption capacity as high as 2 mmol/g can be reached within 2 h. ► The adsorption isotherm is best described by Langmuir model. ► The kinetic data fit well to the pseudo-second-order rate expression. ► The optimized condition is pH of 6–9 and initial concentration of over 300 mg/L.In this study, a novel complexing membrane was synthesized for boron removal from aqueous solution. A glycopolymer, poly(2-gluconamidoethyl methacrylate) (PGAMA), was grafted onto the chloromethylated polysulfone (CMPSF) microporous membrane via surface-initiated ATRP (SIATRP). The glycosylated PSF (GlyPSF) membrane was characterized by attenuated total refection-Flourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). It was demonstrated that PGAMA was successfully anchored onto the membrane surface and the grafting yield can be tuned in a wide range up to 5.9 mg/cm2 by varying the polymerization time. The complexing membrane can adsorb boron rapidly with the equilibrium reached within 2 h and has a remarkable high boron adsorption capacity higher than 2.0 mmol/g at optimized conditions. Freundlich, Langmuir, and Dubinin–Radushkevich adsorption isotherms were applied, and the data were best described by Langmuir model. Kinetic data were analyzed, and the data fitted very well to the pseudo-second-order rate expression. The optimal pH for boron uptake is in a wide range of 6–9, and the optimal initial boron concentration is over 300 mg/L. Studies of ionic strength effects indicated the formation of inner-sphere surface complexes. The complexed boron can be leached quantitatively under acid condition.
Keywords: Surface-initiated atom transfer radical polymerization (SI-ATRP); Polysulfone (PSF) membrane; Complexing membrane; Boron removal; Surface glycosylation;
Stöber silica particles as basis for redox modifications: Particle shape, size, polydispersity, and porosity by Nicolas Plumeré; Adrian Ruff; Bernd Speiser; Verena Feldmann; Hermann A. Mayer (208-219).
Display Omitted► Silica nanoparticles of various diameters are prepared and characterized. ► The Stöber sol–gel process is optimized for desired particle properties. ► High water concentrations and calcination result in nonporous particles. ► Low polydispersity results under conditions where T has a weak effect on diameter. ► Surface area analysis confirms sphericity, nonporosity and low polydispersity.The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800 nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600 °C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol–gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques.
Keywords: Silica nanoparticles; Stöber sol–gel process; Synthesis; Properties; Isolation;
Synthesis of porous poly(styrene-co-acrylic acid) microspheres through one-step soap-free emulsion polymerization: Whys and wherefores by Rui Yan; Yaoyao Zhang; Xiaohui Wang; Jianxiong Xu; Da Wang; Wangqing Zhang (220-225).
Display Omitted► One-step soap-free emulsion polymerization for the synthesis of porous microspheres is reported. ► Phase separation between the hydrophilic and the hydrophobic segments is ascribed to the pore formation. ► 150–240 nm porous microspheres containing 4–25 nm pores are synthesized. ► Advantages including well-controlled pore size and convenience are demonstrated.Synthesis of porous poly(styrene-co-acrylic acid) (PS-co-PAA) microspheres through one-step soap-free emulsion polymerization is reported. Various porous PS-co-PAA microspheres with the particle size ranging from 150 to 240 nm and with the pore size ranging from 4 to 25 nm are fabricated. The porous structure of the microspheres is confirmed by the transmission electron microscopy measurement and Brunauer–Emmett–Teller (BET) analysis. The reason for synthesis of the porous PS-co-PAA microspheres is discussed, and the phase separation between the encapsulated hydrophilic poly(acrylic acid) segment and the hydrophobic polystyrene domain within the PS-co-PAA microspheres is ascribed to the pore formation. The present synthesis of the porous PS-co-PAA microspheres is anticipated to be a new and convenient way to fabricate porous polymeric particles.
Keywords: Emulsion polymerization; Microspheres; Phase separation; Porous microspheres; Poly(styrene-co-acrylic acid);
Formation of macroporous self-assembled hydrogels through cryogelation of Fmoc–Phe–Phe by Dmitriy Berillo; Bo Mattiasson; Igor Yu. Galaev; Harald Kirsebom (226-230).
Display Omitted► We study the formation of macroporous hydrogels from self-assembly of dipeptides. ► The porosity of the gels was obtained though gelation at an apparently frozen state. ► The gel phase of the material consisted of densely packed fibres formed by the dipeptides.In this study, it was found that macroporous hydrogels were formed when self-assembly of fluorenyl-9-methoxycarbonyl (Fmoc)–diphenylalanine (Phe–Phe) peptides was induced using glucono-δ-lactone (GdL) in apparently frozen samples. Formed cryogels exhibited a heterogeneous structure with pore walls of densely packed fibres of assembled dipeptides and pores in the range 10–100 μm. Hydrogels formed from the same composition above the freezing point exhibited a homogenous structure without any apparent porosity. The formed gels were characterised using microscopy techniques, CD-spectroscopy and stress sweeps. The cryogels exhibited less mechanical strength than the hydrogels that might be due to the heterogeneous structure of the former. It appeared that the self-assembled peptide both in the cryo- and hydrogel maintained the β-sheet structure commonly attributed to these.
Keywords: Hydrogels; Macroporous; Dipeptides; Peptides; Self-assembly;
Contribution of capillary electrophoresis to an integrated vision of humic substances size and charge characterizations by Fanny d'Orlyé; Pascal E. Reiller (231-240).
Display Omitted► Humic substances (HS) are characterized in terms of R H, size, and charge in CZE. ► HS are of nanometric dimension whatever the ionic strength and alkaline counter-ion. ► Electrophoretic mobilities are related to electrolyte composition. ► Weak HS–alkali metal interactions affect HS electrophoretic transport.The physicochemical properties of three different humic substances (HS) are probed using capillary zone electrophoresis in alkaline carbonate buffers, pH 10. Special attention is drawn to the impact of the electrolyte ionic strength and counter-ion nature, chosen within the alkali-metal series, on HS electrophoretic mobility. Taylor–Aris dispersion analysis provides insights into the hydrodynamic radius (R H) distributions of HS. The smallest characterized entities are of nanometric dimensions, showing neither ionic strength– nor alkali-metal-induced aggregation. These results are compared with the entities evidenced in dynamic light scattering measurements, the size of which is two order of magnitude higher, ca. 100 nm. The extended Onsager model provides a reasonable description of measured electrophoretic mobilities in the ionic strength range 1–50 mM, thus allowing the estimation of limiting mobilities and ionic charge numbers for the different HS samples. An unexpected HS electrophoretic mobility increase (in absolute value) is observed in the order Li+ < Na+ < K+ < Cs+ and discussed either in terms of retarding forces or in terms of ion–ion interactions.
Keywords: Humic acids; Fulvic acids; Capillary electrophoresis; Size; Charge; Alkali-metal ion;
Preparation and characterization of polystyrene/Ag core–shell microspheres – A bio-inspired poly(dopamine) approach by Wencai Wang; Yi Jiang; Shipeng Wen; Li Liu; Liqun Zhang (241-249).
Display Omitted► A facile and versatile method is proposed to prepare PS/Ag core–shell microspheres. ► PDA is used as chelating and reducing agent for the formation of catalytic sites (Ag). ► The PS/Ag microspheres show good conductivity and low effective density. ► Hollow Ag microspheres were prepared by removing the PS core through calcination.A facile and versatile method using a biopolymer as a chelating agent for silver ions and as a reducing agent for the formation of catalytic sites is proposed to prepare polystyrene (PS)/Ag core–shell microspheres. More specifically, the core–shell microspheres were fabricated by electroless plating after the formation of poly(dopamine) (PDA) on the surface of PS microspheres through in situ spontaneous oxidative polymerization of dopamine. The PS–PDA microspheres were characterized by SEM, XPS, and TGA. The results showed that a uniform PDA layer was formed on the PS microsphere surface and the thickness of the PDA layer could be well controlled by varying the concentration of dopamine solution. The PDA layer was used as a chelating agent for silver ions, as a reducing agent for the formation of catalytic sites by reducing the silver ions into silver nanoparticles, and as an adhesion layer between the PS microspheres and silver layer. SEM and XRD results indicate that the diameter of the silver nanoparticles decreased with the increase in the thickness of the PDA layer. The silver nanoparticles could form a continuous and compact silver layer on the surface of the PS microspheres. Furthermore, the PS–PDA/Ag core–shell microspheres showed a good conductivity of 10 S/cm and a low effective density of 1.8 g/cm3, much lower than the corresponding values for block silver. Finally, hollow silver microspheres could be prepared by removing the PS core through calcination. SEM images showed that the hollow Ag microspheres remained unbroken and retained the spherical shape.
Keywords: PS microspheres; Dopamine; Silver; Surface;
The synthesis, structure, optical and photocatalytic properties of silica-coated cadmium sulfide nanocomposites of different shapes by Nidhi Gupta; Bonamali Pal (250-256).
Display Omitted► Synthesis of cubic and hexagonal CdS nanostructures in silica matrix. ► Fabrication of core (CdS nanorod)-shell (SiO2) hybrid nanocomposite. ► CdS nanorod surface area (21.2 m2/g) is improved after SiO2 (42.3 m2/g) coating. ► Strong emission of CdS nanostructures is quenched after SiO2 layer deposition. ► Photoactivity is markedly enhanced after SiO2 shell formation over CdS nanorod.The CdS nanostructure undergoes photochemical dissolution, and hence, the photocatalytic activity deteriorates with light irradiation time. A thin layer of silica coating over CdS surface may prevent the photocorrosion and coalescence of quantum size CdS particles. Hence, we synthesized SiO2@CdS nanocomposites of different shapes and characterized them by XRD, HRTEM, EDX, SAED, BET surface area measurement and absorption and emission study. The dispersion of spherical CdS (Cd-2.62 at% and S-2.33 at%) nanoparticles of cubic crystal structure into thick amorphous SiO2 (43.79 at%) matrix is demonstrated here. The fabrication of core (CdS)-shell (SiO2) structure (SiO2@CdS) consisting of CdS nanorod (Cd-19.79 at% and S-22.90 at%) core (length ∼126 nm and width ∼6 nm) having characteristic lattice fringes of hexagonal crystals and thin SiO2 (12.81 at%) shell (thickness = 1–1.4 nm) is successfully achieved for the first time. The surface area (21.2 m2/g) of CdS nanorod (aspect ratio = 21) is found to increase (42.3 m2/g) after SiO2 coating. The photoluminescence of CdS nanosphere (485 nm) and nanorod (501 nm) is highly quenched after SiO2 layer formation. The superior photocatalytic activity of SiO2@CdS composites for the benzaldehyde oxidation under UV irradiation has been displayed.
Keywords: Core–shell structure; CdS nanorod core; SiO2 thin shell; SiO2@CdS nanocomposites; Photostable CdS particles; CdS photoreactivity;
Effect of plasma etching on photoluminescence of SnO x /Sn nanoparticles deposited on DOPC lipid membrane by Hyeun Hwan An; Seung Jae Lee; Seung Ha Baek; Won Bae Han; Young Ho Kim; Chong Seung Yoon; Sang Hee Suh (257-262).
Display Omitted► A monolayer of oxide-covered Sn nanoparticles was fabricated using a lipid membrane. ► Enhanced photoluminescence from the SnO x /Sn monolayer was observed by plasma etching. ► The enhancement stemmed from the removal of the surface lipid layer and additional defect states. ► Photoluminescence enhancement can be also induced by hydration of the nanoparticles.The photoluminescence characteristic of the SnO x /Sn nanoparticles deposited on a solid supported liquid–crystalline phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine) membrane was probed after plasma etching the nanoparticle monolayer. It was shown that the plasma etching of the nanoparticle surface greatly altered the particle morphology and enhanced the PL effect, especially when the particle size was below 10 nm in spite of strong presence of surrounding carbon. The enhancement mainly stemmed from the growth of a new PL peak due to the additional defect states produced on the nanoparticle surface by the plasma etching. It was also shown that hydrating the SnO x /Sn nanoparticles similarly improved the PL response of the nanoparticles as the hydration produced an additional oxygen-rich oxide layer on the particle surface.
Keywords: Photoluminescence; Tin oxide nanoparticles; Phospholipid; Lipid membrane;
Hydrated phosphorus oxyacids alone and adsorbed on nanosilica by V.M. Gun'ko; L.P. Morozova; A.A. Turova; A.V. Turov; V.E. Gaishun; V.M. Bogatyrev; V.V. Turov (263-272).
Display Omitted► Effects of structural characteristics of nanosilicas on the interfacial behavior of phosphorus oxyacids. ► Confined space effects on the characteristics of bound water/acid solution. ► Effects of silica on interaction of phosphorus oxyacids with water. ► The δ H value as a measure of associativity of interfacial water and aqueous solution of acids.Low-temperature 1Н NMR spectroscopy was used to study states of water bound to phosphoric and phosphonic acids (phosporus oxyacids, POA) alone or adsorbed onto nanosilica OX-50 (specific surface area S BET = 52 m2/g) or A-300 (S BET = 297 m2/g). Concentrated solutions or weakly hydrated solid POA or dried silica/POA powders placed in CCl4 medium are characterized by different temperature dependences of the chemical shift of the proton resonance (δ H) because of partial dissociation of PO–H bonds strongly affected by water amounts and temperature. NMR cryoporometry results show that both small water clusters and nanodomains are present at the interfaces of hydrated solid POA and silica/POA powders. Quantum chemical calculations of the 1H NMR spectra demonstrate the influence of POA/water cluster structure and dissociation of the PO–H bonds on the δ H values.
Keywords: Fumed silica; 1H NMR spectra; Phosphoric acid; Phosphonic acid; Bound water; Interfacial phenomena;
Effect of pullulan/poly(vinyl alcohol) blend system on the montmorillonite structure with property characterization of electrospun pullulan/poly(vinyl alcohol)/montmorillonite nanofibers by Md. Shahidul Islam; Jeong Hyun Yeum; Ajoy Kumar Das (273-281).
.Display Omitted► PULL/PVA/MMT nanofibers fabrication. ► Good interactions between PULL and PVA caused by possibly hydrogen bonds. ► Different PULL/PVA blend ratios cause different MMT structures. ► Thermal stability of PULL/PVA/MMT nanofibers is influenced by MMT structures.Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets.
Keywords: Pullulan; Poly(vinyl alcohol); Montmorillonite; Nanofiber;
Magnetic assistance highly sensitive protein assay based on surface-enhanced resonance Raman scattering by Lei Chen; Wonjin Hong; Zhinan Guo; Youngjo Sa; Xu Wang; Young Mee Jung; Bing Zhao (282-286).
Display Omitted► Development of AgMNPs as protein carrier. ► External magnetic field induced the aggregation of AgMNPs can provide high SERRS enhancement. ► This is a promising potential of applications for quantitatively immunoassays based on SERRS.A simple and effective surface-enhanced Raman scattering (SERS)-based protocol for the detection of protein–small molecule interactions has been developed. We employed silver-coated magnetic particles (AgMNPs), which can provide high SERS activity as a protein carrier to capture a small molecule. Combining magnetic separation and the SERS method for protein detection, highly reproducible SERS spectra of a protein–small molecule complex can be obtained with high sensitivity. This time-saving method employs an external magnetic field to induce the AgMNPs to aggregate to increase the amount of atto610-biotin/avidin complex in a unit area with the SERS enhancement. Because of the contribution of the AgMNP aggregation to the SERS, this protocol has great potential for practical high-throughput detection of the protein–small molecule complex and the antigen–antibody immunocomplex.
Keywords: SERS; AgMNPs; Avidin; Protein detection;
Photo-responsive properties of poly(NIPAM-co-AAc) microgel particles with absorbed, hydrophobically modified organic salts by Kaizhong Fan; Melanie Bradley; Brian Vincent (287-291).
Display Omitted► UV irradiation triggered the release of an amphiphile from a microgel dispersion. ► The release of an amphiphile is reversible. ► The azobenzene-based amphiphile undergoes trans to cis isomerization. ► The cmc of the amphiphile increases significantly upon UV irradiation.The absorption of two hydrophobically modified organic salts (HMOSs), containing azobenzene units, into poly(N-isopropylacrylamide-co-acrylic acid) microgel particles has been studied at pH 8 and 20 °C. These dispersions were then irradiated with UV light (wavelength 365 nm) for 10 min to observe the effect on the microgel particle properties, such as the adsorbed amount of the HMOS, the particle size, and the electrophoretic mobility. We show that irradiation of these dispersions with UV light can lead to induced, partial desorption of the HMOS molecules, with concomitant changes in the size and electrophoretic mobility of the microgel particles. This is due to a conformational switch (trans-form to cis-form) in the HMOS molecules, which reduces the strength of the hydrophobic interaction between the HMOS molecules and the isopropyl moieties within the microgel network. Moreover, the original absorbed amounts, size, and electrophoretic mobility values can be largely restored after storage in the dark for extended periods.
Keywords: Microgels; Azobenzene; Absorption; Photo-responsive; Controlled release;
Vesicles prepared with the complex salts dioctadecyldimethylammonium polyacrylates by Fernanda Rosa Alves; Watson Loh (292-300).
Display Omitted► Vesicles of the complex salts dioctadecyldimethylammonium polyacrylates were prepared and characterized. ► Properties of these vesicles do not differ much from those with monomeric counterions. ► Multilamellar vesicles are favored by the presence of the polymeric counterion. ► This methodology can be used to prepare vesicles with controlled composition containing polymeric counterions.The effect of a polymeric counterion on the thermotropic behavior of sonicated vesicles formed by complex salts in aqueous solution and with decanol (C10OH) and tetradecanol (C14OH) was investigated. The complex salts were prepared with dioctadecyldimethylammonium bromide (DODAB) and polyacrylic acids (PAA, containing 30 or 6000 repeating units), being referred to as DODAPA30 and DODAPA6000. Vesicles containing polymeric counterions presented higher contents of multilamellar vesicles that were dependent on the complex salt concentration and on the counterion chain length. For comparison, studies were performed with DODAAc, with the counterion acetate, resulting in the formation of mostly unilamellar vesicles, as expected due greater dissociation, leading to greater electrical repulsion between bilayers. Mixtures of these complex salts and DODAX (where X = acetate or bromide) were also investigated with respect to their vesicles thermotropic behavior and size. This study opens the possibility of applying the methodology of direct complex salt preparation (as opposed to mixing the surfactant and polymeric components) to produce vesicles with controlled composition and properties.
Keywords: Vesicle; Complex salts; Polyacrylate–dioctadecyldimethylammonium;
Cyclodextrin induced switch between heterolytic and homolytic dediazoniation mechanisms by Alejandra Fernández-Alonso; Carlos Bravo-Díaz (301-309).
Display Omitted► We studied the reaction of 4-nitrobenzenediazonium ions with cyclodextrins at pH < 3. ► In the absence of cyclodextrin, the main reaction pathway is heterolytic D N + A N mechanism. ► Addition of cyclodextrin increases the rate of reaction and promotes homolytic dediazoniation. ► Addition of sodium dodecylsulfate blocks the cyclodextrin cavity inhibiting the reaction.We have investigated the kinetics and mechanism of dediazoniation of 4-nitrobenzenediazonium (4NBD) tetrafluoroborate in the presence of α-cyclodextrin, α-CD, and γ-cyclodextrin, γ-CD, under acidic (HCl, pH = 2) conditions by employing a combination of spectrometric and chromatographic techniques. In the absence of CDs, dediazoniation follows first-order kinetics, with t 1/2 = 22,000 s at T = 60 °C, but addition of small amounts of either α-CD or γ-CD leads to more rapid but not first-order kinetics with t 1/2 ∼ 400 s when [α-CD] = 20 [4NBD] or [γ-CD] = 15 [4NBD]. Analyses of reaction mixtures by HPLC indicate that three main dediazoniation products are formed depending on the particular experimental conditions. These are 4-nitrophenol, ArOH, nitrobenzene, ArH, and 4-nitrochlorobenzene, ArCl. In the absence of CDs, the main dediazoniation product is the substitution product ArOH, but on increasing the concentration of CD, the reduction product ArH becomes predominant at the expense of ArOH, indicating that a switch between the heterolytic and homolytic reaction mechanisms take place under acidic conditions, where little significant ionization of the OH groups of the CDs takes place (pK a ≈ 12). Addition of the surfactant sodium dodecylsulfate, SDS, blocks the CD cavity inhibiting 4NBD dediazoniation and decreasing the yields of ArH with a concomitant increase in that of ArOH, suggesting that 4NBD ions form an inclusion complex prior to reacting with the OH groups of the CDs. This O-coupling reaction leads to the formation of a highly unstable Z-diazo ether adduct that cannot isomerize to the much more stable E-isomer because of the geometric restrictions imposed by the CD cavity, splitting homolitically.
Keywords: Diazo ether; Arenediazonium ions; Cyclodextrin; Surfactants; Kinetics;
Surface characterization and liquid crystal alignment behavior of comb-like poly(oxyethylene)/poly(3-hexylthiophene) blend films by Eun-Ho Sohn; Sung Hyun Kim; Mongryong Lee; Kigook Song (310-318).
The surface properties of comb-like polymer/poly(3-hexylthiophene) blends were investigated and correlated with the liquid crystal alignment behaviors on the polymer blend films.Display Omitted► Surface properties of comb-like polymer/polythiophene blends were investigated. ► LC alignment behavior of the blend films was correlated with the surface properties. ► Surface energy or contact angle is not suitable to explain the LC alignment behavior. ► The comb-like polymer part on the blend films predominantly affects the LC alignment.The blend surfaces of poly[oxy(n-decylsulfonylmethyl)ethylene] (CH3–10SE) and poly (3-hexylthiophene) (P3HT) with different weight ratios were prepared by spin coating the polymer solution mixtures. In this study, their surface properties such as surface morphology, chemical composition, molecular structure, and wettability were systematically studied and correlated with liquid crystal (LC) alignment behaviors on the blend films. Therefore, we found that CH3–10SE part with a well-ordered side chain structure predominantly affects the both of wettability and LC alignment behavior of the blend films while there was no clear association between the wettability and the LC alignment behavior.
Keywords: Polymer blend; Surface property; Liquid crystal alignment behavior; Comb-like polymer; Poly(3-hexylthiophene);
Oil-in-water Pickering emulsion destabilisation at low particle concentrations by Jessica Avendaño Juárez; Catherine P. Whitby (319-325).
Display Omitted► Emulsions were formed at low particle concentrations that do not stabilise drops. ► Drops flocculate and ripen before becoming susceptible to coalescence. ► Destabilisation is linked to the aggregate structures formed by particle coagulation.Droplet evolution in unstable, dilute oil-in-water Pickering emulsions was characterised using a combination of light scattering, confocal microscopy and rheology. Emulsions were formed at concentrations of silanised fumed silica particles that are not sufficient to prevent destabilisation. The key result is that destabilisation initially occurs via a combination of droplet flocculation and permeation. Close contact between the drops enhances oil transfer from smaller drops to the larger ones. The large drops swell over time until the attached particle density is insufficient to protect the drops against coalescence. Examination of the emulsion microstructure revealed the relationship between drop stability and the structural characteristics of the aggregates formed due to coagulation of the silica particles in the emulsions. The implications of these results for controlling Pickering emulsion stability are discussed.
Keywords: Particle-stabilised emulsion; Pickering emulsion; Emulsion destabilisation;
Binary mixtures with novel monomeric and dimeric surfactants: Influence of the head group nature and number of hydrophobic chains on non-ideality by Victoria Isabel Martín; Amalia Rodríguez; María del Mar Graciani; María Luisa Moyá (326-335).
In this work, the influence of the nature of the head group and the number of hydrophobic chains on the non-ideal behavior of binary surfactant mixtures has been investigated.Display Omitted► Binary mixtures of surfactants were studied. ► ROESY experiments provided information about the mixed micelles. ► Three theoretical approaches were applied for investigating the mixtures behavior. ► Micellar growth of mixed micelles was investigated.The micellization and micellar growth in the mixtures of N,N-dimethyl, N-phenyl,N-dodecylammonium bromide, PH12, N,N-dimethyl,N-ciclohexylmethyl,N-dodecylammonium bromide, CH12, and their two dimeric counterparts m-dimethylphenyl-α-ω-bis(dodecyldimethylammonium) bromide, 12PH12, and m-dimethylciclohexyl-α-ω-bis(dodecyldimethylammonium) bromide, 12CH12, with dodecyltrimethylammoniumbromide, DTAB, and with N-decanoyl N-methylglucamide, MEGA10, were investigated at 303 K. Circular dichroism, CD, experiments showed the formation of mixed micelles. Two-dimensional, 2D, rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments indicated that the arrangement of the rings in the pure and mixed micelles is similar, with the rings bent into the micelle interior avoiding contact with water. Application of different theoretical approaches shows that PH12 and CH12 mixtures with DTAB and with MEGA10 behave almost ideally. The binary systems of 12PH12 and 12CH12 with DTAB and with MEGA10 show a non-ideal behavior. An increment in the solution mole fraction of MEGA10 and DTAB diminishes the tendency of the micellar aggregates to grow.
Keywords: Surfactant mixtures; MEGA10; DTAB; Cationic surfactants; Monomeric; Dimeric; Phenyl ring; Cyclohexyl ring; Non-ideal; ROESY;
Effect of water-soluble polymers, polyethylene glycol and poly(vinylpyrrolidone), on the gelation of aqueous micellar solutions of Pluronic copolymer F127 by Nágila M.P.S. Ricardo; Nadja M.P.S. Ricardo; Flávia de M.L.L. Costa; Francisco W.A. Bezerra; Chiraphon Chaibundit; Daniel Hermida-Merino; Barnaby W. Greenland; Stefano Burattini; Ian W. Hamley; S. Keith Nixon; Stephen G. Yeates (336-341).
Display Omitted► Gelation of aqueous micellar solutions of Pluronic copolymer F127. ► Addition of polyethylene glycol (PEG) increases the critical gel concentration (cgc). ► Addition of poly(vinylpyrrolidone) (PVP) may decrease the cgc. ► The elastic modulus of the gel is much reduced on adding PEG, less so on adding PVP. ► 30 wt% F127 gel has the face-centered cubic structure for both polymers.The micellization of F127 (E98P67E98) in dilute aqueous solutions of polyethylene glycol (PEG6000 and PEG35000) and poly(vinylpyrrolidone) (PVP K30 and PVP K90) is studied. The average hydrodynamic radius (r h,app) obtained from the dynamic light scattering technique increased with increase in PEG concentration but decreased on addition of PVP, results which are consistent with interaction of the micelles with PEG and the formation of micelles clusters, but no such interaction occurs with PVP. Tube inversion was used to determine the onset of gelation. The critical concentration of F127 for gelation increased on addition of PEG and of PVP K30 but decreased on addition of PVP K90. Small-angle X-ray scattering (SAXS) was used to show that the 30 wt% F127 gel structure (fcc) was independent of polymer type and concentration, as was the d-spacing and so the micelle hard-sphere radius. The maximum elastic modulus ( G max ′ ) of 30 wt% F127 decreased from its value for water alone as PEG was added, but was little changed by adding PVP. These results are consistent with the packed-micelles in the 30 wt% F127 gel being effectively isolated from the polymer solution on the microscale while, especially for the PEG, being mixed on the macroscale.
Keywords: F127; Water soluble polymer; Micelle; Gel; Modulus;
Role of surfactants on the approaching velocity of two small emulsion drops by Krassimir D. Danov; Simeon D. Stoyanov; Nikolay K. Vitanov; Ivan B. Ivanov (342-355).
Display Omitted► We model the hydrodynamic interaction between two approaching spherical drops. ► The model accounts for the surface material properties (rheology and diffusivity). ► The role of surfactants soluble in the continuous and/or disperse phases is studied. ► Increasing the surfactant chain length will decrease the interfacial mobility. ► The surfactants soluble in the disperse phase decrease the emulsion stability.Here we present the exact solution of two approaching spherical droplets problem, at small Reynolds and Peclet numbers, taking into account surface shear and dilatational viscosities, Gibbs elasticity, surface and bulk diffusivities due to the presence of surfactant in both disperse and continuous phases. For large interparticle distances, the drag force coefficient, f, increases only about 50% from fully mobile to tangentially immobile interfaces, while at small distances, f can differ several orders of magnitude. There is significant influence of the degree of surface coverage, θ, on hydrodynamic resistance β for insoluble surfactant monolayers. When the surfactant is soluble only in the continuous phase the bulk diffusion suppresses the Marangoni effect only for very low values of θ, while in reverse situation, the bulk diffusion from the drop phase is more efficient and the hydrodynamic resistance is lower. Surfactants with low value of the critical micelle concentration (CMC) make the interfaces tangentially immobile, while large CMC surfactants cannot suppress interfacial mobility, which lowers the hydrodynamic resistance between drops. For micron-sized droplets the interfacial viscosities practically block the surface mobility and they approach each other as solid spheres with high values of the drag coefficient.
Keywords: Hydrodynamic resistance between two approaching drops; Tangentially mobile surfaces; Soluble and insoluble surfactants; Interfacial rheology effect; Flocculation rate of emulsion droplets; Small Reynolds and Peclet numbers;
Thermodynamic and structural characterization of a mixed perfluorocarbon–phospholipid ternary monolayer surfactant system by Ala'a F. Eftaiha; Sophie M.K. Brunet; Matthew F. Paige (356-365).
Display Omitted► Ternary phospholipid–perfluorcarbon mixed monolayers are fully miscible. ► Head group interactions between DPPC and perfluorocarbon enhance film stability. ► Langmuir–Blodgett films contain multilayer aggregates enriched in phospholipid.Pulmonary lung surfactant is a mixture of surfactants that reduces surface tension during respiration. Perfluorinated surfactants have potential applications for artificial lung surfactant formulations, but the interactions that exist between these compounds and phospholipids in surfactant monolayer mixtures are poorly understood. We report here, for the first time, a detailed thermodynamic and structural characterization of a minimal pulmonary lung surfactant model system that is based on a ternary phospholipid–perfluorocarbon mixture. Langmuir and Langmuir–Blodgett monolayers of binary and ternary mixtures of the surfactants 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and perfluorooctadecanoic acid (C18F) have been studied in terms of miscibility, elasticity and film structure. The extent of surfactant miscibility and elasticity has been evaluated via Gibbs excess free energies of mixing and isothermal compressibilities. Film structure has been studied by a combination of atomic force microscopy and fluorescence microscopy. Combined thermodynamic and microscopy data indicate that the ternary monolayer films were fully miscible, with the mixed films being more stable than their pure individual components alone, and that film compressibility is minimally improved by the addition of perfluorocarbons to the phospholipids. The importance of these results is discussed in context of these mixtures' potential applications in pulmonary lung surfactant formulations.
Keywords: Surfactants; Miscibility; Thermodynamics; Perfluorocarbon; Phosphatidylcholine; Phosphatidylglycerol; Monolayer; Langmuir–Blodgett;
Thermally stable organically modified layered silicates based on alkyl imidazolium salts by Shailesh K. Goswami; Smita Ghosh; Lon J. Mathias (366-371).
Display Omitted► Synthesis of novel imidazolium salts with a variety of functional groups. ► Organic modification of natural and synthetic layered silicates using imidazolium salts. ► Organically modified layered silicates have much higher thermal stability.A series of imidazolium salts having various substituents and functional groups were synthesized and characterized by FTIR and NMR spectroscopy. Organic modification of natural and synthetic layered silicates involving montmorillonite (MMT), LAPONITE® (lap), and synthetic mica (mica) was carried out by ion-exchange reaction. The obtained organo-clays were characterized by FTIR and powder X-ray diffraction techniques. Results indicate that these organically modified clays have much higher thermal stabilities compared to their corresponding imidazolium halides. It was also observed from TGA analysis that thermal stability does not depend on the functional group present at the 3-position of the imidazolium salts. These studies strongly supports premise that the removal of halide is necessary to improve the thermal stability of the organo-clay produced.
Keywords: Imidazolium surfactant; Organo-clay; PLSNs; Thermal stability; TGA; XRD;
Enhancement of DNA compaction by negatively charged nanoparticles: Effect of nanoparticle size and surfactant chain length by Sergii Rudiuk; Kenichi Yoshikawa; Damien Baigl (372-377).
Display Omitted► Negatively charged nanoparticles enhance DNA compaction by cationic surfactants. ► Enhancement is optimal for large nanoparticles and small surfactant chain length. ► Preaggregation of surfactants on nanoparticles promotes cooperative binding to DNA.We study the compaction of genomic DNA by a series of alkyltrimethylammonium bromide surfactants having different hydrocarbon chain lengths n: dodecyl-(DTAB, n = 12), tetradecyl-(TTAB, n = 14) and hexadecyl-(CTAB, n = 16), in the absence and in the presence of negatively charged silica nanoparticles (NPs) with a diameter in the range 15–100 nm. We show that NPs greatly enhance the ability of all cationic surfactants to induce DNA compaction and that this enhancement increases with an increase in NP diameter. In the absence of NP, the ability of cationic surfactants to induce DNA compaction increases with an increase in n. Conversely, in the presence of NPs, the enhancement of DNA compaction increases with a decrease in n. Therefore, although CTAB is the most efficient surfactant to compact DNA, maximal enhancement by NPs is obtained for the largest NP diameter (here, 100 nm) and the smallest surfactant chain length (here, DTAB). We suggest a mechanism where the preaggregation of surfactants on NP surface mediated by electrostatic interactions promotes cooperative binding to DNA and thus enhances the ability of surfactants to compact DNA. We show that the amplitude of enhancement is correlated with the difference between the surfactant concentration corresponding to aggregation on DNA alone and that corresponding to the onset of adsorption on nanoparticles.
Keywords: DNA; Nanoparticles; DNA compaction; Surfactant; Higher-order structure; Fluorescence microscopy;
Hydrophobin coated boehmite nanoparticles stabilizing oil in water emulsions by Martin Reger; Heinz Hoffmann (378-386).
Display Omitted► Novel hydrophobin coated boehmite nanoparticles as emulsifiers. ► Long-term stable and homogenous Pickering emulsions. ► Emulsion stability due to attraction of the covered oil droplets. ► Gel-like properties of the emulsions obtained by formation of a three-dimensional network.Hydrophobin coated boehmite nanoparticles have been used to establish tooth-paste like, homogenous emulsions. The surface-modified nanoparticles were simply obtained by mixing aqueous solutions of cationic boehmite particles with the anionic hydrophobin H Star Protein B® (HPB). Surface tension measurements clearly show that 1 wt.% boehmite binds up to 1 wt.% HPB. The strong interaction and aggregation of hydrophobin coated boehmite nanoparticles was proven by Cryo-TEM measurements, too. Interestingly, the combined use of 0.5 wt.% HPB and 0.5 wt.% boehmite as emulsifying agents resulted in very stable, homogenous, high internal phase emulsions (65 wt.% oil) that are stable over months. The established emulsions have also been characterized by rheological measurements. Storage moduli of more than 1000 Pa are characteristic for their high gel-like properties. Furthermore, light microscopy showed an average droplet size close to 1 μm with low polydispersity. Cryo-SEM confirmed that the hydrophobin coated nanoparticles are located at the interface of the oil droplets and therefore stabilize the emulsion systems.
Keywords: Boehmite; Hydrophobin; Nanoparticles; Pickering emulsion; Synergism;
Self-assembled aggregates of amphiphilic perylene diimide–based semiconductor molecules: Effect of morphology on conductivity by Yanli Chen; Yajuan Feng; Jian Gao; Marcel Bouvet (387-394).
Display Omitted► PDI 1 and 2 were fabricated into organic nanostructures with different morphology. ► Excellent conductivities of the PDI aggregates from methanol are obtained. ► PDI 1 nanobelts exhibited an unexpected high conductivity of 3.3 × 10−3 S cm−1.Two amphiphilic perylenetetracarboxylic diimide derivatives modified with different side chains at imide nitrogen, N-n-hexyl-N′-(2-hydroxyethyl)-1,7-di(4′-t-butyl)phenoxy-perylene-3,4:9,10-tetracarboxylic diimide (PDI 1) and N,N′-di(2-hydroxyethyl)-1,7-di(4′-t-butyl)phenoxy-perylene-3,4:9,10-tetracarboxylic diimide (PDI 2), were fabricated into organic nanostructures via solution-phase self-assembly. Their self-assembling properties in methanol and n-hexane have been comparatively studied by electronic absorption, fluorescence, and Fourier transform infrared spectroscopy (FT-IR). The morphologies and structures of the self-assemblies were examined by scanning electronic microscopy (SEM), atomic force microscopy (AFM), as well as X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due to the presence of different number of hydroxyethyl groups in the molecule of PDI 1 and PDI 2, the self-assembly of the two molecules in methanol and n-hexane results in nanostructures with distinctly different morphology as follows: nanobelts and nanoleaves for PDI 1 and nanobelt dendrites and nanosheets for PDI 2, respectively. Analysis of the spectral change for the aggregates relative to that of monomeric PDI in solution revealed that in polar and apolar solvents, both nanobelts and nanoleaves precipitated from PDI 1 adopt the H aggregation mode, whereas nanobelt dendrites and nanosheets from PDI 2 adopt H and J aggregation mode, respectively, implying the effect of both side-chain substituent and solvent on tuning the intermolecular stacking. Furthermore, the conductivity of the aggregates of either PDI 1 or PDI 2 from methanol is more than ca. 1 order of magnitude higher than those from n-hexane. In particular, the well-defined, one-dimensional (1D) nanobelts of PDI 1 show excellent semiconducting property with the electrical conductivity as high as 3.3 × 10−3 S cm−1, which might serve as promising candidates for applications in nano-electronics.
Keywords: Perylenetetracarboxy diimides; Self-assembly; Morphology; Molecular material; Conductivity;
Formation of multiple water-in-ionic liquid-in-water emulsions by Jianshen Li; Jianling Zhang; Buxing Han; Yueju Zhao; Guanying Yang (395-399).
Display Omitted► Water-in-ionic liquid-in-water multiple emulsions have been prepared for the first time. ► These novel multiple emulsions involve no volatile organic solvent. ► The water-in-ionic liquid-in-water multiple emulsions have potential applications in various fields.Emulsions composed of an ionic liquid (IL) 3-methyl-1-octylimidazolium hexafluorophosphate, water, and surfactant TX-100 (poly(ethylene glycol)-tert-octylphenyl) were studied by laser confocal scanning microscopy, stability determination and electrical conductivity. Multiple water-in-ionic liquid-in-water (W/IL/W) emulsions were formed around water volume fractions ∼0.70. Further studies showed that the W/IL/W multiple emulsions were formed through an inversion between water-in-IL emulsion and IL-in-water emulsion.
Keywords: Ionic liquid; Multiple emulsion; Emulsion inversion;
Synthesis of poly(vinyl acetate–methyl methacrylate) copolymer microspheres using suspension polymerization by Md. Shahidul Islam; Jeong Hyun Yeum; Ajoy Kumar Das (400-405).
Display Omitted► Poly(vinyl acetate–methyl methacrylate) copolymer microspheres. ► Suspension polymerization. ► Obtained copolymer microspheres which have 200 μm average diameter. ► Copolymers show higher thermal stability than homopolymers.Poly(vinyl acetate–methyl methacrylate) (VAc–MMA) copolymer microspheres were prepared using suspension polymerization at low temperature initiated with 2,2′-azobis(2,4-dimethyl valeronitrile) (ADMVN). The poly(VAc–MMA) copolymer microspheres can be used over a large area where homopolymers, polyvinyl acetate (PVAc) and methyl methacrylate (PMMA) microspheres are capable of being put to use. The prepared microspheres were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Obtained copolymer microspheres which have 200 μm average diameter and higher thermal stability than those of homopolymer.
Keywords: Suspension polymerization; Poly(vinyl acetate–methyl methacrylate) copolymer; Microspheres;
The co-effect of Sb and Nb on the SCR performance of the V2O5/TiO2 catalyst by Xuesen Du; Xiang Gao; Yincheng Fu; Feng Gao; Zhongyang Luo; Kefa Cen (406-412).
Display Omitted► Both Nb and Sb can increase the activity of V2O5/TiO2 catalyst, and Nb can improve the N2 selectivity. ► The co-doping of Sb and Nb showed higher improving effect than the single doping of Sb or Nb. ► The Sb―Nb co-doped V2O5/TiO2 catalyst had a better H2O resistance than the V2O5/TiO2 catalyst. ► The presence of SO2 could improve the activity of Sb―Nb-doped catalyst at the absence of water vapor.The effect of the Sb and Nb additives on the V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3 was investigated. The experimental results show that either Nb or Sb can improve the activity of V2O5/TiO2 catalyst. Higher Nb loading led to higher N2 selectivity. The co-doping of Sb and Nb showed higher improving effect than the single doping of Sb or Nb. The V2O5/TiO2 catalyst doped with Sb and Nb had a better H2O resistance than the V2O5/TiO2 catalyst. The addition of Sb and Nb also enhance the resistance of the V2O5/TiO2 catalyst to K2O poisoning. The catalysts were characterized by BET, XRD, TEM, and XPS. The results showed that the active components of V, Sb, and Nb were well interacting with each other. The coexistence of Sb and Nb will enhance the redox ability and surface acidity and thus promote the SCR performance.
Keywords: Selective catalytic reduction; NH3; NO; V2O5; Nb; Sb;
In situ electro-deposition of Pt micro-nano clusters on the surface of {[PMo12O40]3−/PAMAM} n multilayer composite films and their electrocatalytic activities regarding methanol oxidation by Zhong-Shui Li; Shen Lin; Zu-liang Chen; Yuan-De Shi; Xiao-Mei Huang (413-419).
Display Omitted► LBL technique is used to fabricate the organic–inorganic composite films. ► Composite films are constructed from polyoxometalates and PAMAM. ► Composite films are used as a new matrix for electro-deposition of Pt clusters. ► Pt micro-nano clusters show the unique flower-like cluster structure. ► Composite films supported Pt clusters show good catalysis for methanol oxidation.The {[PMo12O40]3−/PAMAM} n multilayer films are prepared by LBL electrostatic assembly technique, and their uniform and homogeneous traits have been verified by cyclic voltammetry. The {[PMo12O40]3−/PAMAM} n multilayer films with PAMAM as the outmost layer, having an open structure and exhibiting good penetrability for the solvent molecules at low pH, are used as matrices for electro-deposition of Pt micro-nano clusters in situ. X-ray photoelectron spectroscopy (XPS) analysis and field emission scanning electron microscope (FE-SEM) characterization show that the unique Pt micro-nano clusters with flower-like structure have been immobilized on the surface of {[PMo12O40]3−/PAMAM} n multilayer films. The morphologies of Pt micro-nano clusters are influenced by electro-deposition conditions such as deposition potential, deposition time, and the number of layers of {[PMo12O40]3−/PAMAM} n multilayer films. Pt-clusters-{PMo12/PAMAM}3 composite films demonstrate good electrocatalytic activities regarding methanol oxidation and improved tolerance of CO.
Keywords: LBL assembly; Polyoxometalates; PAMAM; Pt micro-nano clusters; Methanol oxidation; Electrocatalysis;
Influence of Ca2+ on tetracycline adsorption on montmorillonite by M. Eugenia Parolo; Marcelo J. Avena; Gisela R. Pettinari; Miria T. Baschini (420-426).
Display Omitted► The adsorption of TC on montmorillonite was studied as a function of pH and Ca2+. ► In the presence of Ca2+, two different TC adsorption processes took place. ► TC adsorption became independent of Ca2+ concentration only at pH 5. ► XRD and TEM indicate that TC was intercalated in the interlayer space.The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca2+ concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca2+, TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca2+, at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH < 5, and thus, TC adsorption decreased by increasing total Ca2+ concentration. On the contrary, Ca-bridging was the prevailing process at pH > 5, and thus, TC adsorption increased by increasing Ca2+ concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca2+ concentration at this pH. For TC adsorption on Ca2+-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca2+ was close to 1 in the pH range of 5–9, indicating an important participation of Ca2+ in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC.
Keywords: Adsorption; Intercalation; Clays; Tetracycline; Antibiotics;
Pattern of adsorption isotherms in Ono–Kondo coordinates by Panita Sumanatrakul; Sarah Abaza; Gregory L. Aranovich; Chayanoot Sangwichien; Marc D. Donohue (427-433).
Display Omitted► Ono–Kondo (OK) theory is used to study intermolecular interactions in adsorbed phase. ► General pattern of isotherms in OK coordinates is determined and analyzed. ► The slope of OK graphs varies from positive at low pressure to negative at high pressure. ► The linear sections of OK graphs indicate the limits of the classical model. ► In the limit of high pressures, adsorbate is compressed at any value of Henry's constant.The Ono–Kondo lattice density functional theory is used to analyze adsorbate–adsorbate interactions for supercritical systems. In prior work, this approach has been used to study intermolecular interactions in subcritical adsorbed phases, and this has included the study of adsorbate–adsorbate repulsions in the regime of adsorption compression. In this paper, we present the general pattern of adsorption isotherms in Ono–Kondo coordinates; this has not been done in the past. For this purpose, experimental isotherms for adsorption of supercritical fluids (including nitrogen, methane, and carbon dioxide) are plotted in Ono–Kondo coordinates. In addition, we performed Grand Canonical Monte Carlo simulations of adsorption for Lennard-Jones molecules and plotted isotherms in Ono–Kondo coordinates. Our results indicate a pattern of isotherms with regimes of adsorbate–adsorbate attractions at low surface coverage and adsorbate–adsorbate repulsions at high surface coverage. When the generalized Ono–Kondo model is used over a wide range of pressures – from low pressures of the Henry's law regime to supercritical pressures – the slope of the isotherm varies from positive at low pressures to negative at high pressures. The linear sections of these graphs show when the adsorbate–adsorbate interaction energies are approximately constant. When these linear sections have negative slopes, it indicates that the system is in a state of adsorption compression.
Keywords: Gas–solid equilibrium; Ono–Kondo model; Adsorption compression; Adsorbate–adsorbate repulsions;
Reversibility of cadmium sorption to calcite revisited by Z. Li; A. Hofmann; M. Wolthers; P. Thomas (434-442).
Display Omitted► Cd2+ sorption/desorption to/from calcite studied at CO2–H2O–CaCO3 equilibrium. ► Cd2+ sorption to calcite is shown to be reversible. ► Sorption and desorption rates have same magnitude. ► The change in reaction kinetics with time is similar for sorption and desorption. ► Sorption reversibility may be linked to counter-ion density in the EDL.Cadmium sorption to calcite was studied in aqueous solution at calco-carbonic (CO2–H2O–CaCO3) equilibrium and at concentrations below the solubility product of otavite (<10−7 mol L−1). Experiments were conducted in a stirred flow-through reactor, lasting for 15 and 60 h at flow rates of 1.6 and 0.5 mL min−1, respectively. Under both flow conditions, the cadmium breakthrough curves reached steady state after a flow time of about 50 reactor volumes, but different calcite saturation levels were achieved, which implied time-dependent sorption rates. Desorption of cadmium was induced by switching from Cd-containing to Cd-free solution in the reactor inflow. Reversibility of sorption was then evaluated by comparing amounts sorbed and desorbed over identical time intervals. On average, the desorption/sorption ratio was 95 ± 10%. Desorption rates were close to those for sorption and showed the same time dependency: Initially, rates were fast and slowed down with time. "Irreversible" surface reactions such as solid-solution formation could not be inferred. In previous research, cadmium sorption was often shown to be partly irreversible. We surmise that calcite surface ripening is conditioned by the concentration of lattice-building ions in the EDL. At calco-carbonic equilibrium, these ion concentrations at the surface are lowest. Therefore, irreversible binding of cadmium is not favoured.
Keywords: Stirred flow-through reactor; Cd2+ sorption; Cd2+ desorption; Calcite; Calco-carbonic equilibrium; Sorption rates; Reversible sorption; Irreversible sorption;
Amphiphilic block copolymer-stabilized PtRu nanoparticles highly dispersed on multi-walled carbon nanotube for methanol oxidation by Dao-Jun Guo; Peng Cai; Jin-Mao You (443-446).
Display Omitted► An efficient method is presented for modify MWCNTs with PtRu nanoparticles. ► Synthesis of PtRu nanoparticles using P123 is a very mild method. ► This is a development for synthesis method of fuel cell catalyst.We report a one-pot synthesis of amphiphilic block copolymer-stabilized PtRu nanoparticle modified multi-walled carbon nanotubes (MWCNTs) using RuCl3·xH2O and H2PtCl6·6H2O as ruthenium and platinum sources, and block copolymer poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) as stabilizer agent. PtRu alloyed nanoparticles with an average diameter of 4.6 nm are well decorated homogeneously on the exterior surfaces of the MWCNTs. The electrochemical catalytic activity for methanol oxidation of PtRu/MWCNTs and commercial PtRu/C (E-TEK) is comparatively investigated using cyclic voltammetry and chronoamperometry. It is revealed that the PtRu nanoparticle modified MWCNT samples display an enhanced electrochemical catalytic activity than commercial PtRu/C electrode. These results show that PtRu nanoparticles may find applications to fuel cells.
Keywords: Electrocatalyst; Fuel cells; Methanol oxidation; Nanoparticles;
Short range order at the amorphous TiO2–water interface probed by silicic acid adsorption and interfacial oligomerization: An ATR-IR and 29Si MAS-NMR study by Peter J. Swedlund; Yantao Song; Zoran D. Zujovic; Michél K. Nieuwoudt; Andreas Hermann; Grant J. McIntosh (447-455).
Display Omitted► ATR-IR and 29Si NMR spectra of H4SiO4 on the amorphous TiO2 surface are reported. ► Sorption and oligomerization on TiO2 were similar to that on an amorphous iron oxide. ► Linear silicate oligomers are formed on disordered oxide surfaces. ► This result is interpreted using a structural model for the amorphous TiO2.Adsorption and oligomerization of H4SiO4 at the amorphous TiO2–aqueous interface were studied using in situ Attenuated Total Reflectance Infrared (ATR-IR) and ex situ solid state 29Si nuclear magnetic resonance (NMR). The ATR-IR spectra indicate that a monomeric silicate species is present at low silicate surface concentration (Γ Si). Above a threshold Γ Si linear silicate oligomers are formed and these oligomers dominate the surface at high Γ Si. Interestingly the ATR-IR spectra of H4SiO4 on the TiO2 surface are very similar to those previously observed on the poorly ordered iron oxide phase ferrihydrite. The 29Si NMR spectrum of silicate on the TiO2 surface shows the presence of Si in three states with chemical shifts corresponding to isolated monomers (Q 0), the ends of linear oligomers (Q 1) and the middle of linear oligomers (Q 2). The ratio of the area of the Q 1 and Q 2 peaks was ≈2:1 which is consistent with the proposed formation of linear silicate trimers by insertion of a solution H4SiO4 between adjacent suitably orientated adsorbed silicate monomers. A structural interpretation indicates that the observed interfacial silicate oligomerization behavior is a general phenomenon whereby bidentate silicate monomers on oxide surfaces are disposed towards forming linear oligomers by condensation reactions involving their two terminal Si–OH groups. The high surface curvature of nanometer sized spheres inhibits the formation of interfacial silicates with a higher degree of polymerization.
Keywords: Titanium dioxide; Silicic acid; Adsorption; Polymerization; Attenuated Total Reflectance Infrared; 29Si solid state NMR;
The effects of promoters of K and Zr on the mesoporous carbon supported cobalt catalysts for Fischer–Tropsch synthesis by Liang Chen; Guoxia Song; Yuchuan Fu; Jianyi Shen (456-461).
Display Omitted► 15%Co/MC was significantly more active than 15%Co/AC for Fischer–Tropsch synthesis. ► Addition of K and Zr significantly affected Fischer–Tropsch activity of 15%Co/MC. ► Addition of K and Zr significantly changed the acidity and basicity of 15%Co/MC. ► Surface acidity and basicity affected the adsorption of CO and H2 on supported Co. ► Relative adsorption strengths of CO and H2 on Co affected Fischer–Tropsch activity.The mesoporous carbon supported cobalt catalyst (15%Co/MC) was found to be more active and selective to C 5 + than the traditionally activated carbon supported one (15%Co/AC) for the Fischer–Tropsch synthesis (FTS). The addition of small amount of K2O and ZrO2 significantly affected the FTS behavior of 15%Co/MC. The addition of 1% K inhibited the FTS activity dramatically, while the addition of 3% Zr increased the FTS activity significantly. The addition of K2O decreased the surface acidity while increased the surface basicity of 15%Co/MC, resulting in the increased heat of adsorption of CO and substantially decreased heat of adsorption of H2 on Co. In contrast, the addition of ZrO2 increased the surface acidity and heat of adsorption of H2 on Co. The FTS activity was found to be related to the ratio of heats for the adsorption of CO and H2 on the catalysts 15%Co/MC, 15%Co–1%K/MC and 15%Co–3%Zr/MC. The highest FTS activity was obtained on the catalyst with the heat ratio of 1.2.
Keywords: Fischer–Tropsch synthesis; Mesoporous carbon supported Co; K and Zr promoters; Surface acidity and basicity; Adsorption heats;
Vanadium oxide intercalated with polyelectrolytes: Novel layered hybrids with anion exchange properties by Fernando J. Quites; Chiara Bisio; Rita de Cássia G. Vinhas; Richard Landers; Leonardo Marchese; Heloise O. Pastore (462-469).
Display Omitted► Hybrids were developed by the insertion of PDDA and PAH in V2O5 interlayer space. ► The anion exchange hybrids were used to host an anionic cyanine dye. ► Interlayer space of V2O5 expands from 0.44 to 1.40 nm and 1.80 nm for PDDA and PAH. ► XPS and DR UV–Vis–NIR revealed that a part of V5+ was reduced to V4+ by intercalation.Novel anion exchange hybrid materials were developed by the insertion of poly(diallymethylammonium chloride) (PDDACl) and poly(allylamine hydrochloride) (PAHCl) polyelectrolytes into V2O5 interlayer spaces using hydrothermal treatment and were used to host an anionic cyanine dye. A systematic study of the hybrid material synthesis by direct in situ reaction of PDDACl and PAHCl polycations with V2O5 powders showed that the interlayer space of V2O5 expands from 0.44 nm to 1.40 nm and 1.80 nm upon intercalation of PDDACl and PAHCl polyelectrolytes, respectively. X-ray photoelectron spectroscopy and DR UV–Vis–NIR spectroscopy revealed that some V5+ sites were reduced to V4+ during the intercalation of the polyelectrolytes, these acted as both charge balancing entities for the negative oxide sheets and carriers for exchange sites located in the V2O5 interlayer space. The interlayer separation is consistent with the existence of coiled conformation of the polycations. The hybrid materials produced [PDDACl]0.24[PDDA]0.29V2O5 and [PAHCl]0.28[PAH]0.47V2O5, exhibited approximately 45.0% and 37.0% of chloride ions still available for anionic exchange, respectively. These materials were used to encapsulate a cyanine anionic dye. The presence of the dye was evidenced in the [PDDACl]0.24[PDDA]0.29V2O5 by significant fluorescence, with emission peak centered at 617 nm.
Keywords: Vanadium oxide; Polyelectrolytes; Intercalation reactions; Redox reactions; Cyanine dyes; PDDACl; PAHCl; Anionic exchanger;
Humidity adsorption kinetics of a trypsin gel film by Salih Okur; Cagatay Ceylan; Evren Culcular (470-473).
Display Omitted► BPTG was adsorbed on a gold coated Quartz Crystal Microbalance. ► QCM was used to investigate the humidity sensing properties of the BPTG film. ► The response of the humidity sensor was explained using the Langmuir model. ► Adsorption and desorption rates, the equilibrium constants and their Gibbs Free Energies were obtained.This study focuses on the humidity adsorption kinetics of an isopropanol-induced and pH-triggered bovine pancreatic trypsin gel (BPTG). The BPTG was adsorbed on a gold coated Quartz Crystal Microbalance (QCM) substrate with a thickness of 376 nm. The morphology of the film was characterized using Atomic Force Microscopy (AFM). QCM was used to investigate the humidity sensing properties of the BPTG film. The response of the humidity sensor was explained using the Langmuir model. The average values of adsorption and desorption rates between 11% RH (relative humidity) and 97% RH were calculated as 2482.5 M−1 s−1 and 0.02 s−1, respectively. The equilibrium constant and average Gibbs Free Energy of humidity adsorption and desorption cycles were obtained as 133,000 and −11.8 kJ/mol, respectively.
Keywords: Trypsin; Gelation; Thin film; Humidity; Quartz crystal microbalance; Atomic force microscopy;
Packing effects on argon and methanol adsorption inside graphitic cylindrical and slit pores: A GCMC simulation study by Zhongjun Liu; Toshihide Horikawa; D.D. Do; D. Nicholson (474-487).
Display Omitted► Packing configurations of non-polar and polar fluids in pores of different shapes. ► Linear, zigzag and helical packing configurations are observed for argon. ► Zigzag configuration is preferred by methanol to maximize the hydrogen bonding. ► Adsorbed fluid is denser in cylinder than in comparable slit. ► Packing manners have effects on the behaviour of the isosteric heat versus loading.Using Grand Canonical Monte Carlo simulation, we have studied the effects of confinement on argon and methanol adsorption in graphitic cylindrical and slit pores. Linear chain, zigzag and incomplete helical packing are observed for argon adsorption in cylindrical pores. However, for methanol adsorption different features appear because the electrostatic interactions favour configurations that maximize the hydrogen bonding among methanol molecules. We have found zigzag chains with hydrogen-bonded structures for methanol adsorption in cylindrical and slit pores. To investigate how dense the adsorbed phase is and how many molecules could be packed per unit physical volume of the solid, we consider two different definitions of pore density; one based on the physical volume and the other on the accessible volume. That based on accessible volume gives a measure of the fluid density, while that based on the physical volume gives a measure of how much adsorbate can be stored per unit volume of the adsorbent. It is found that the adsorbate is denser in cylindrical pores, but that slit pores can pack more molecules per unit solid volume. We also discuss the effects on the isosteric heat of argon and methanol of pore size, pore geometry and loading.
Keywords: Helical packing; Isosteric heat; GCMC simulation; Accessible volume; Confinement effects; Methanol adsorption;
Synthesis of four different antimony(III) O,O′-dialkyldithiophosphates: Characterization by 31P CP/MAS NMR, single-crystal X-ray diffraction, and adsorption at a stibnite surface (Sb2S3) by Anna-Carin Larsson; Maxim A. Ivanov; Andrey V. Gerasimenko; Alexander V. Ivanov (488-495).
Display Omitted► Crystal structure determination of [Sb{S2P(O-cyclo-C6H11)2}3]·1/3 C2H5OH. ► 31P CP/MAS NMR chemical shift anisotropy parameters for [Sb{(S2P(OR)2}3] complexes are determined. ► 31P CP/MAS NMR data on dithiophosphate ligands surface adsorbed on synthetic stibnite suggest a bridging coordination.Four different dialkyldithiophosphate (DTP) ions, (RO)2PSS− (R = C3H7, iso-C3H7, iso-C4H9, and cyclo-C6H11), have been adsorbed on the surface of synthetically prepared stibnite, Sb2S3, and studied by means of 31P CP/MAS NMR. Corresponding individual [Sb{S2P(OR)2}3] complexes have also been synthesized and used for comparison with the surface-adsorbed DTP species. The results show that a low concentration of collector at the surface leads to a chemisorbed monolayer of DTP on the mineral surface. At high concentration of DTP, a surface precipitate of Sb(DTP)3 is formed. 31P CP/MAS NMR and chemical shift anisotropy data indicate that the S―P―S bite angle of the chemisorbed DTP groups on the surface is larger than in the corresponding precipitated complexes and the coordination of the ligands differs. Using single-crystal X-ray diffraction technique, the molecular structure of a solvated form of crystalline O,O′-di-cyclo-hexyldithiophosphate antimony(III) complex has been resolved. In this novel molecular structure, the central antimony atom S,S′-anisobidentately coordinates three structurally non-equivalent DTP groups, and therefore, the geometry of the [SbS6] chromophore can be approximated by a distorted octahedron. Besides that, useful correlations between 31P CSA parameters and structural data on this complex were also established.
Keywords: Dithiophosphate; Antimony(III); Molecular structure; CP/MAS NMR; Chemical shift anisotropy; Chemisorption; Synthetic stibnite; Sb2S3;
Sorption of selenium(IV) and selenium(VI) onto synthetic pyrite (FeS2): Spectroscopic and microscopic analyses by Dong Suk Han; Bill Batchelor; Ahmed Abdel-Wahab (496-504).
Display Omitted► More strong evidences for Se(IV) reduction than Se(VI) on the pyrite surface. ► Reduction of Se(IV) via disproportionation of the surface-bound sulfur. ► Phase image of AFM showed more heterogeneity of Se(IV)-contacted pyrite.Pyrite was hydrothermally synthesized and used to remove Se(IV) and Se(VI) selectively from solution. Surface analyses of pyrite before and after contact with Se(IV) and Se(VI) were conducted using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). All solid samples were acquired by allowing 3.1 mmol/L of Se(IV) or Se(VI) to react with 1 g/L of pyrite for 1, 15, or 30 days. The XPS spectra were fitted using the XPSPEAK program that applies a Gaussian Lorentzian function. The fitted spectra indicate that Se(IV) more strongly reacts with the surface-bound S than with the surface-bound Fe of pyrite. However, there is no apparent evidence of surface reaction with Se(VI). Specifically, fitted XPS spectra showed the presence of sulfide and tetrathionate on the surface, indicating that sulfur ( S 2 2 - ) at the surface of pyrite can be both oxidized and reduced after contact with Se(IV). This occurs via surface disproportionation, possibly resulting in the formation of surface precipitates. Evidence for the formation of precipitates was seen in SEM and AFM images that showed rod-like particles and a phase image with higher voltage. In contrast, there were no important changes in the pyrite after contact with Se(VI) over a period of 30 days.
Keywords: Selenite; Selenate; Sorption; Precipitation; Pyrite;
Batch and column study: Sorption of perfluorinated surfactants from water and cosolvent systems by Amberlite XAD resins by Feng Xiao; Kerry Jade Davidsavor; Sangyoo Park; Michio Nakayama; Brian Ray Phillips (505-511).
Display Omitted► Sorption of five long-chain PFCs by XAD-7HP and XAD-2 was investigated. ► XAD-7HP performance was compared with other resins reported in previous studies. ► XAD-7 HP is an excellent sorbent for concentrating or removing PFCs.Amberlite XAD resins have been employed to a great extent as the sorbent for removing or concentrating organic compounds from different matrices. We present for the first time a systematic study on the sorption of perfluorochemical (PFC) surfactants, an emerging class of environmental contaminants, by XAD-7HP (moderately polar) and XAD-2 (nonpolar). The results show that XAD-7HP can strongly sorb PFCs at circumneutral pH; the isotherm-determined linear sorption coefficient can reach 106 L/kg. On the other hand, the sorption coefficient for XAD-2 was two orders of magnitude lower than that for XAD-7HP. PFC sorption on XAD-7HP increased with an increase of the perfluorocarbon chain length of PFC and a decrease of the solution pH, indicating the importance of hydrophobic and electrostatic effects. The sorption coefficient for XAD-7HP reduced markedly with increasing fraction of the organic cosolvent (methanol) in the water–cosolvent mixture; however, the trend could not be predicted by a log-linear cosolvency model. Furthermore, the statistical analysis of column test results showed that after regeneration XAD-7HP can be used at least eight times without significant loss of performance. Finally, the experimental results imply that XAD-7HP sorption of shorter-chained PFCs (⩽5 perfluorinated carbons) from water can be thermodynamically favorable.
Keywords: Perfluoroalkyl acids; PFOS; PFOA; Polymeric sorbent; Breakthrough;
In situ kinetic study of zinc sulfide activation using a quartz crystal microbalance with dissipation (QCM-D) by Fucheng Teng; Qingxia Liu; Hongbo Zeng (512-520).
Schematic drawing of the silver activation process of ZnS sensor using a quartz crystal microbalance with dissipation (QCM-D).Display Omitted► Investigation of the activation kinetics of zinc sulfide by silver using a QCM-D. ► Identification of two distinct (logarithmic and parabolic) stages on silver activation. ► Demonstration of the presence of silver and its penetration into the bulk ZnS. ► Introduction of a new approach to study in situ surface adsorption and activation.We have studied the activation kinetics of zinc sulfide (ZnS) using silver as an activator by a quartz crystal microbalance with dissipation (QCM-D). The zinc sulfide coating on QCM-D sensor was shown to have similar crystallographic structure, composition, and surface properties as nature sphalerite through the characterization of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and xanthate adsorption measurement using QCM-D. The activation of ZnS sensor by silver was confirmed by the mass increase in ZnS sensor coupled with subsequent xanthate adsorption during QCM-D measurement, the change of surface wettability, and the presence of Ag2S on the surface. Two distinct stages on the silver uptake vs. time curve were identified and fitted well by a logarithmic function for the initial stage and a parabolic law in the later stage, which agrees with the two-stage zinc–silver reaction kinetics reported previously. Argon sputtering followed by XPS measurement on the ZnS surface demonstrated the penetration of silver into the bulk ZnS after activation. The present study is the first of its kind to apply the QCM-D technique to investigate sphalerite activation, which introduces a new in situ approach to investigate surface adsorption and activation in many mineral processes and surface modifications.
Keywords: Zinc sulfide activation; QCM-D; Activation kinetics; Surface adsorption;
Preparation of activated carbon derived from cotton linter fibers by fused NaOH activation and its application for oxytetracycline (OTC) adsorption by Yuanyuan Sun; Qinyan Yue; Baoyu Gao; Qian Li; Lihui Huang; Fujiang Yao; Xing Xu (521-527).
Display Omitted► Fused NaOH activation is used to prepare cotton linter-based activated carbon. ► Activated carbon from cotton linter fibers had a large surface area of 2143 m2/g. ► Carbon from cotton linter fibers had a predominantly microporous structure. ► Competitive adsorption took place in the weakly acidic to neutral conditions. ► Strong acid or strong basic hindered the adsorption by electrostatic repulsion.The objective of this research is to produce high surface area–activated carbon derived from cotton linter fibers by fused NaOH activation and to examine the feasibility of removing oxytetracycline (OTC) from aqueous solution. The cotton linter fibers activated carbon (CLAC) was characterized by N2 adsorption/desorption isotherms, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The results showed that CLAC had a predominantly microporous structure with a large surface area of 2143 m2/g. The adsorption system followed pseudo-second-order kinetic model, and equilibrium was achieved within 24 h. The equilibrium data were described well by Langmuir isotherm. Thermodynamic study showed that the adsorption was exothermic reaction at low concentration and became endothermic nature with the concentration increasing. Competitive adsorption took place in the weakly acidic to neutral conditions. Under the strong acidity or strong alkaline condition, the adsorption of the oxytetracycline was hindered by electrostatic repulsion. The adsorption mechanism depended on the pH of the solutions as well as the pK a of the oxytetracycline.
Keywords: Activated carbon; Cotton linter fibers; Fused NaOH activation; Oxytetracycline;
Use of X-ray absorption near edge structure (XANES) to identify physisorption and chemisorption of phosphate onto ferrihydrite-modified diatomite by Wenhui Xiong; Jian Peng; Yongfeng Hu (528-532).
Display Omitted► Chemisorption occurs together with physisorption during phosphorus adsorption onto ferrihydrite-modified diatomite. ► Chemisorption occurs in the bulk of ferrihydrite-modified diatomite (between 50 nm and 5 μm). ► Phosphorus physisorption occurs at the zone of ferrihydrite-modified diatomite shallower than 50 nm.This paper presents a novel technique integrating bulk-sensitive and surface-sensitive XANES methods to distinguish between physisorption and chemisorption for phosphate adsorption onto ferrihydrite-modified diatomite (FHMD). XANES P K-edge, L-edge, and Fe M-edge spectra were obtained for reference samples (K2HPO4 and FePO4·2H2O) and test samples (phosphate adsorbed onto FHMD (FHMD-Ps) and Si-containing ferrihydrite (FHYD-Ps)). A resolvable pre-edge peak in the P K-edge spectra of FHMD-Ps and FHYD-Ps provided direct evidence for the formation of P–O–Fe(III) coordination and the occurrence of chemisorption. The resemblance between the P L-edge spectra of K2HPO4 and FHMD-Ps and the marked difference between the spectra of FHMD-Ps and FePO4·2H2O indicated the intact existence of the adsorbate and the adsorbent. The similarity between Fe M-edge spectra of FHMD and FHMD-Ps and the difference between the spectra of FHMD-Ps and FePO4·2H2O confirmed the findings from P L-edge analyses. Therefore, chemisorption and physisorption coexisted during phosphate adsorption onto FHMD. Phosphate chemisorption occurred in the deeper zone of FHMD (from 50 nm to 5 μm); whereas physisorption occurred in the zone of FHMD shallower than 50 nm since the probing depth of XANES P K-edge method is 5 μm and that of P L-edge and Fe M-edge methods is 50 nm.
Keywords: Ferrihydrite-modified diatomite; XANES; Phosphate adsorption; Chemisorption; Physisorption;
Antibody–antigen interaction on polystyrene: An in situ ellipsometric study by Olof Svensson; Thomas Arnebrant (533-539).
Display Omitted► Ellipsometry was used to monitor the binding of antibodies (IgG) to polystyrene. ► Time resolved values of the adsorbed amount and thickness are presented. ► A structure for the adsorbed antibody layers is proposed. ► Mixed human IgG and anti-human IgG layers were assembled. ► The stability of the adsorbed IgG layers was addressed.The objective of this investigation was to monitor the adsorption of antibodies to polystyrene surfaces using ellipsometry. Commercial polystyrene slides used for solid state diagnostics were selected as substrates and the adsorption of three different antibodies (human IgG, bovine IgG and goat anti-human IgG) were evaluated. Based on theoretical models describing the ellipsometric data, it was concluded that the adsorption of antibodies should result in layers that are sufficiently thick to be able to monitor the adsorption in terms of adsorbed amount and thickness of the layer with a reasonable precision. The experimental results confirmed this assumption and values of 2.0–2.3 mg/m2 were detected for the adsorbed amount with a corresponding thickness of 10–16 nm. It was furthermore found that the antibodies bound irreversibly with respect to rinsing with protein-free solutions. In additional experiments, the consecutive incubation of human IgG and anti-human IgG was investigated. These results showed that, on average, approximately half of the surface immobilized anti-human IgG molecules are capable of binding to human IgG during its incubation. From the consecutive binding experiments it could also be concluded that antibodies present in the polyclonal anti-human IgG preparation were capable of binding to around four different epitopes on the human IgG. A final set of experiments addressed the stability of adsorbed human IgG layers with respect to drying and incubation with surfactant. The results revealed that the adsorbed antibody layer is relatively resistant to these treatments.
Keywords: Adsorption; Antibody; Polystyrene; Ellipsometry; Immunoassays; ELISA;
Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide by Yuan Gao; Yan Li; Liang Zhang; Hui Huang; Junjie Hu; Syed Mazhar Shah; Xingguang Su (540-546).
Display Omitted► GO was used as an adsorbent for tetracycline removal from the aqueous solution. ► Tetracyclines strongly deposited on GO via π–π interaction and cation–π bonding. ► The adsorption isotherms fit Langmuir model and Freundlich model well. ► The adsorption kinetics and effect of pH were studied in detail.Significant concerns have been raised over pollution of antibiotics including tetracyclines in aquatic environments in recent years. Graphene oxide (GO) is a potential effective absorbent for tetracycline antibiotics and can be used to remove them from aqueous solution. Tetracycline strongly deposited on the GO surface via π–π interaction and cation–π bonding. The adsorption isotherm fits Langmuir and Temkin models well, and the theoretical maximum of adsorption capacity calculated by Langmuir model is 313 mg g−1, which is approximately in a close agreement with the measured data. The kinetics of adsorption fits pseudo-second-order model perfectly, and it has a better rate constant of sorption (k), 0.065 g mg−1 h−1, than other adsorbents. The adsorption capacities of tetracycline on GO decreased with the increase in pH or Na+ concentration. The adsorption isotherms of oxytetracycline and doxycycline on GO were discussed and compared.
Keywords: Graphene oxide; Tetracycline; Antibiotics; Adsorption;
Sorption of metal cations by alginate-based biosorbents. On the correct determination of the thermodynamic parameters by Wojciech Plazinski (547-551).
Display Omitted► Thermodynamics of metal ions binding by alginate-based biosorbents was studied. ► System- and model-related factors influence the apparent thermodynamic parameters. ► These effects were qualitatively and quantitatively described.The paper is focused on the problem of interpretation of the experimental data related to the thermodynamics of metal ions binding by alginate-based biosorbents. When considering the thermodynamic parameters (i.e., changes in the enthalpy and entropy values; ΔH and ΔS, respectively), one can observe large discrepancies between their values even if the considered systems have very similar features. For instance, the binding of copper, cadmium, and lead can be entropy-driven, enthalpy-driven or both entropy- and enthalpy-driven, depending on the considered report. The aim of this paper is to find the reason for this paradox and to discuss the problem of interpretation of the data being usually the base for estimating ΔH and ΔS values. It appears that both numerous "technical" (e.g., pH, ionic strength) and model-related (e.g., monodentate vs. bidentate binding models) parameters can seriously influence the obtained values of thermodynamic parameters. The significance of these two types of factors is discussed in qualitative and quantitative manners. The proposed methods of distinguishing between the "apparent" and the "real" ΔH and ΔS values can be also related to other types of sorption/adsorption systems.
Keywords: Entropy; Enthalpy; Gibbs free energy; Adsorption; Biosorption; Heavy metal ion; Modeling; van't Hoff plot;
High physisorption affinity of water molecules to the hydroxylated aluminum oxide (0 0 1) surface by Shigeharu Kittaka; Keisuke Yamaguchi; Shuichi Takahara (552-557).
Monolayer water on the (0 0 1) Al2O3 at 298.1 K.Display Omitted► High affinity of α-Al2O3 (0 0 1) surface to water was confirmed by GCMC simulation. ► Bilayer hexagonal structure was formed by adsorption on the Al2O3 (0 0 1) surface. ► Much higher interaction of water with the α-Al2O3 surface than with Cr2O3.The adsorption mechanism of water on the hydroxylated (0 0 1) plane of α-Al2O3 was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al2O3 samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al2O3 surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365 K, which is higher than that on the hydroxylated Cr2O3 surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al2O3 surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al2O3 (0 0 1) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (0 0 1) plane of ice Ih.
Keywords: α-Al2O3; Water adsorption; Monolayer; 2D condensed state; 2D phase diagram; 2D critical point; GCMC simulation; Bilayer structure: hexagonal ring network;
Contact line extraction and length measurements in model sediments and sedimentary rocks by Elena Rodriguez; Maša Prodanović; Steven L. Bryant (558-577).
Display Omitted► Unprecedented description of contact line lengths in porous media. ► Lengths are quantified during drainage and imbibition processes. ► The method for contact line quantification is applicable to any type of porous system. ► Developed algorithm applies to fluid configurations from simulation and experiments.The mechanisms that govern the transport of colloids in the unsaturated zone of soils are still poorly understood, because of the complexity of processes that occur at pore scale. These mechanisms are of specific interest in quantifying water quality with respect to pathogen transport (e.g. Escherichia coli, Cryptosporidium) between the source (e.g. farms) and human users. Besides straining in pore throats and constrictions of smaller or equivalent size, the colloids can be retained at the interfaces between air, water, and grains. Theories competing to explain this mechanism claim that retention can be caused by adhesion at the air–water-interface (AWI) between sediment grains or by straining at the air–water–solid (AWS) contact line. Currently, there are no established methods for the estimation of pathogen retention in unsaturated media because of the intricate influence of AWI and AWS on transport and retention. What is known is that the geometric configuration and connectivity of the aqueous phase is an important factor in unsaturated transport. In this work we develop a computational method based on level set functions to identify and quantify the AWS contact line (in general the non-wetting–wetting–solid contact line) in any porous material. This is the first comprehensive report on contact line measurement for fluid configurations from both level-set method based fluid displacement simulation and imaged experiments. The method is applicable to any type of porous system, as long as the detailed pore scale geometry is available. We calculated the contact line length in model sediments (packs of spheres) as well as in real porous media, whose geometry is taken from high-resolution images of glass bead packs and sedimentary rocks. We observed a strong dependence of contact line length on the geometry of the sediment grains and the arrangement of the air and water phases. These measurements can help determine the relative contribution of the AWS line to pathogen retention.
Keywords: Contact line length; Interfacial area; Colloid retention; Drainage; Imbibition; Level set method; X-ray images; Model sediments;
Hybridization of sugar alcohols into brucite interlayers via a melt intercalation process by Kazuya Morimoto; Kenji Tamura; Tamao Hatta; Seiko Nemoto; Takuya Echigo; Jinhua Ye; Hirohisa Yamada (578-583).
Display Omitted► Novel organic–inorganic hybrids based on brucite have been prepared by melt mixing procedure. ► Brucite-polyol hybrids were successfully prepared by a melt intercalation method. ► Covalent linkage between sugar alcohols and brucite layers was confirmed.We report the preparation of organic-brucite (BR) hybrids using harmless sugar alcohols (xylitol, XYL, and sorbitol, SOR). Since XYL and SOR are solid materials at room temperature, the hybridization was investigated by comparing two separate methods, hydrothermal treatment and melt mixing. BR-sugar alcohol hybrids were successfully prepared by a melt intercalation method at 175 °C. X-ray diffraction and Fourier transform infrared spectroscopy analyses indicated that organic molecules were intercalated into the brucite layers, overcoming the barrier of hydroxyl bonds between the BR layers. Moreover, X-ray photoelectron spectroscopy and thermal analyses showed that the intercalated materials at 175 °C resulted in the formation of covalent Mg–O–C bond linkages on the interlayer surface of BR.
Keywords: Brucite; Xylitol; D-sorbitol; Intercalation;
Durable Lotus-effect surfaces with hierarchical structure using micro- and nanosized hydrophobic silica particles by Daniel Ebert; Bharat Bhushan (584-591).
Display Omitted► Silica particles were used to create hierarchically structured surfaces. ► Wettability was compared for two methods of microstructure fabrication. ► Wettability was measured for hierarchical surfaces to verify Lotus effect. ► Multiscale wear experiments were performed with AFM and tribometer.Surfaces with a very high apparent water contact angle (CA) and low water contact angle hysteresis (CAH) exhibit many useful characteristics, among them extreme water repellency, low drag for fluid flow, and a self-cleaning effect. The leaf of the Lotus plant (Nelumbo nucifera) achieves these properties using a hierarchical structure with roughness on both the micro- and nanoscale. It is of great interest to create durable surfaces with the so-called "Lotus effect" for many important applications. In this study, hierarchically structured surfaces with Lotus-effect properties were fabricated using micro- and nanosized hydrophobic silica particles and a simple spray method. In addition, hierarchically structured surfaces were prepared by spraying a nanoparticulate coating over a micropatterned surface. To examine the similarities between surfaces using microparticles versus a uniform micropattern as the microstructure, CA and CAH were compared across a range of pitch values for the two types of microstructures. Wear experiments were performed using an atomic force microscope (AFM), a ball-on-flat tribometer, and a water jet apparatus to verify multiscale wear resistance. These surfaces have potential uses in engineering applications requiring Lotus-effect properties and high durability.
Keywords: Durability; Lotus; Hierarchical structure; Superhydrophobicity; Wetting transition;
Superior performance of multilayered fluoropolymer films in low voltage electrowetting by Dimitrios P. Papageorgiou; Angeliki Tserepi; Andreas G. Boudouvis; Athanasios G. Papathanasiou (592-598).
Display Omitted► Multilayered hydrophobic dielectric featuring plasma-deposited fluorocarbon interlayer. ► Increased lifetime of the proposed multilayered (composite) top coating. ► High resistance to dielectric breakdown (visible as electrolysis). ► Improvement of electrowetting performance in long term application of AC and DC voltage. ► Persistence of dielectric properties checked by sensitive leakage current measurements.The requirement for low operational voltage in electrowetting devices, met using thin dielectrics, is usually connected with serious material failure issues. Dielectric breakdown (visible as electrolysis) is frequently evident slightly beyond the onset of the contact angle saturation. Here, plasma-enhanced chemical vapor deposition (PECVD) is used to deposit thin fluorocarbon films prior to the spin-coating of Teflon® amorphous fluoropolymer. The resulting multilayered hydrophobic top coating improves the electrowetting performance of the stack, by showing high resistance to dielectric breakdown at high applied voltages and for continuous long term application of DC and AC voltage. Leakage current measurements during electrowetting experiments with the proposed composite coating showed that current remains fairly constant at consecutive electrowetting tests in contrast to plain Teflon® coating in which material degradation is evident by a progressive increase in the leakage current after multiple electrowetting tests. Since the proposed composite coating demonstrates increased resistance to material failure and to dielectric breakdown even at thin configurations, its integration in electrowetting devices may impact their reliability, robustness, and lifetime.
Keywords: Electrowetting on dielectric; Plasma-deposited fluorocarbon; Contact angle saturation;
Superhydrophobicity of electrospray-synthesized fluorinated silica layers by Eun-Kyeong Kim; Chul-Sung Lee; Sang Sub Kim (599-602).
Display Omitted► Superhydrophobic SiO2 layers through a combination of a nanoscale surface roughness and fluorination are realized. ► The nanoscale surface roughness is obtained by electrospraying SiO2 precursor solutions. ► Subsequent fluorination treatment exhibits outstand repellency toward various liquid droplets. ► The SiO2 layers were excellent in light of the durability in water, ultraviolet resistance, and thermal stability.The preparation of superhydrophobic SiO2 layers through a combination of a nanoscale surface roughness and a fluorination treatment is reported. Electrospraying SiO2 precursor solutions that had been prepared by a sol–gel chemical route produced very rough SiO2 layers. Subsequent fluorination treatment with a solution containing trichloro(1H,1H,2H,2H-perfluorooctyl)silane resulted in highly rough, fluorinated SiO2 layers. The fluorinated rough SiO2 layers exhibited excellent repellency toward various liquid droplets. In particular, water repellency of 168° was observed. On the bases of Cassie–Baxter and Young–Dupre equations, the surface fraction and the work of adhesion of the rough, fluorinated SiO2 layers were respectively estimated. In light of the durability in water, ultraviolet resistance, and thermal stability, the superhydrophobic SiO2 layers prepared in this work hold promise in a range of practical applications.
Keywords: Silica; Electrospray; Hydrophobicity; Fluorination;
Facile control of surface wettability in TiO2/poly(methyl methacrylate) composite films by Mengjin Yang; Zengfeng Di; Jung-Kun Lee (603-607).
Display Omitted► We present a facile method to control the water affinity of the surface by composite films. ► The contact angle of PMMA/TiO2 composite films reaches 140° at 50 vol.% of TiO2. ► Preferential orientation of PMMA accounts for the strong hydrophobicity. ► UV light exposure turns the surface of the films to be superhydrophilic. ► Polymer removal and mesoporous structure are responsible for superhydrophilicity.A facile method to produce very hydrophobic surface was developed simply using the mixture of TiO2 nanoparticles and poly(methyl methacrylate) (PMMA). When the volume ratio of TiO2 to PMMA is between 35 vol.% and 50 vol.%, the mixture of two hydrophilic materials became very hydrophobic. Analysis of the molecular structure by infrared spectroscopy shows that the preferential orientation and attachment of a carbonyl group of a polymer molecule to the surface of TiO2 nanoparticles play a critical role in the appearance of the strong hydrophobicity. When this composite was exposed to UV light, PMMA on the surface of the mixture film was decomposed through a photocatalytic reaction and the very hydrophobic surface turned to the superhydrophilic one. The superhydrophilic property of UV-irradiated composite lasts as long as several months. This long lasting superhydrophilicity is ascribed to the porous structure, which provides high roughness and strong capillary interaction. Easy transition from strong hydrophobicity to superhydrophilicity in TiO2/PMMA composites could be applied to designing high contrast hydrophilic/hydrophobic patterns.
Keywords: Ultrahydrophobic; Superhydrophilic; Composite film; Wettability control; High contrast pattern;
Adsorption of modified dextrins on molybdenite: AFM imaging, contact angle, and flotation studies by Audrey Beaussart; Luke Parkinson; Agnieszka Mierczynska-Vasilev; David A. Beattie (608-615).
Display Omitted► Dextrins adsorbing on molybdenite. ► Adsorption characterised by isotherms and AFM imaging. ► Effect of polymers on wettability determined with contact angle measurements and bubble-surface collisions. ► Flotation of molybdenite correlates with polymer morphology, and subsequent effect of polymer on thin film rupture time.The adsorption of three dextrins (a regular wheat dextrin, Dextrin TY, carboxymethyl (CM) Dextrin, and hydroxypropyl (HP) Dextrin) on molybdenite has been investigated using adsorption isotherms, tapping mode atomic force microscopy (TMAFM), contact angle measurements, and dynamic bubble-surface collisions. In addition, the effect of the polymers on the flotation recovery of molybdenite has been determined. The isotherms revealed the importance of molecular weight in determining the adsorbed amounts of the polymers on molybdenite at plateau coverage. TMAFM revealed the morphology of the three polymers, which consisted of randomly dispersed domains with a higher area fraction of surface coverage for the substituted dextrins. The contact angle of polymer-treated molybdenite indicated that polymer layer coverage and hydration influenced the mineral surface hydrophobicity. Bubble-surface collisions indicated that the polymers affected thin film rupture and dewetting rate differently, correlating with differences in the adsorbed layer morphology. Direct correlations were found between the surface coverage of the adsorbed layers, their impact on thin film rupture time, and their impact on flotation recovery, highlighting the paramount role of the polymer morphology in the bubble/particle attachment process and subsequent flotation.
Keywords: Polymer adsorption; Dextrin; Molybdenite; Atomic force microscope; Contact angle; Film rupture; Dewetting; Flotation;
Co-delivery of antigen and a lipophilic anti-inflammatory drug to cells via a tailorable nanocarrier emulsion by Yap Pang Chuan; Bi Yun Zeng; Brendan O'Sullivan; Ranjeny Thomas; Anton P.J. Middelberg (616-624).
Display Omitted► Tailorable nanocarrier emulsion (TNE) prepared in simple sequential addition way. ► Auto-immune-relevant antigen coated onto emulsion stabilized by peptide surfactant. ► Lipophilic drug incorporated into the TNE enables auto-immune disease treatments. ► The TNE was internalized by model antigen-presenting cells. ► TNE uptake successfully downregulated the target protein (NF-κB) in macrophages.Nanotechnology promises new drug carriers that can be tailored to specific applications. Here we report a new approach to drug delivery based on tailorable nanocarrier emulsions (TNEs), motivated by a need to co-deliver a protein antigen and a lipophilic drug for specific inhibition of nuclear factor kappa B (NF-κB) in antigen presenting cells (APCs). Co-delivery for NF-κB inhibition holds promise as a strategy for the treatment of rheumatoid arthritis. We used a highly surface-active peptide (SAP) to prepare a nanosized emulsion having defined surface properties predictable from the SAP sequence. Incorporating the lipophilic drug into the oil phase at the time of emulsion formation enabled its facile packaging. The SAP is depleted from bulk during emulsification, allowing simple subsequent addition of the drug-loaded oil-in-water emulsion to a solution of protein antigen. Decoration of emulsion surface with antigen was achieved via electrostatic deposition. In vitro data showed that the TNE prepared this way was internalized and well-tolerated by model APCs, and that good suppression of NF-κB expression was achieved. This work reports a new type of nanotechnology-based carrier, a TNE, which can potentially be tailored for co-delivery of multiple therapeutic components, and can be made using simple methods using only biocompatible materials.
Keywords: Drug delivery; Emulsion; Nanotechnology; Biosurfactant; Arthritis; Curcumin;
Preparation and characterization of uniform drug particles: Dehydrocholic acid by Amr Ali Mohamed; Egon Matijević (625-628).
Display Omitted► We describe the precipitation of dehydrocholic acid, the only artificial bile acid. ► We show that the same drug can be obtained as uniform particles of two different morphologies. ► Dehydrocholic acid is a main component in drugs treating cholestatic liver disease and other conditions.Two methods for the preparation of uniform dispersions of dehydrocholic acid of different morphologies are described. In the first case, the drug was dissolved in acetone and then re-precipitated by adding a non-solvent (either water or an aqueous stabilizer solution), which yielded rod-like particles. In the second procedure, spheres, consisting of small elongated subunits, were obtained by acidification of basic aqueous solutions of the drug. The resulting particles were characterized in terms of their structure and surface charge characteristics.
Keywords: Colloidal drugs; Dehydrocholic acid; Drug particles;
Structural study on gold nanoparticle functionalized with DNA and its non-cross-linking aggregation by Masahiro Fujita; Yoshizumi Katafuchi; Kazuki Ito; Naoki Kanayama; Tohru Takarada; Mizuo Maeda (629-635).
Non-cross-linking aggregation of DNA-functionalized gold nanoparticles was studied, and the effects of DNA length and core size on the non-cross-linking aggregation were investigated.Display Omitted► Non-cross-linking aggregation of DNA-functionalized gold nanoparticles was characterized. ► The surface distance between gold nanoparticles increases with increasing DNA length. ► The particles with the same core size assemble together without being affected by tethered DNA. ► Even the particles with full-matched DNA can disperse stably depending on core size or DNA length.Hybridization of DNA tethered on colloidal nanoparticles with fully matched complementary one induces the aggregation of the particles in a non-cross-linking configuration. Here, we performed a structural study on DNA-functionalized gold nanoparticle and its non-cross-linking aggregation mainly using synchrotron radiation small-angle X-ray scattering. To understand the non-cross-linking aggregation, the nanoparticles with various DNA lengths and core sizes were used. In the aggregation, the surface distance between the gold nanoparticles increased with the length of DNA duplex, although the increment of the distance per base pair was not constant and showed the tendency to become small with increasing DNA length, meaning the interdigitation of DNA layers. The aggregation was also found to occur between the identical cores, without being affected by tethered DNA. Furthermore, it was proved that the relative increase in DNA length to core size leads to the increase in colloidal stability. Even the nanoparticles with full-matched DNA duplex were dispersed stably. These facts suggested that van der Waals interaction between core particles rather than end-to-end stacking between DNA duplexes is a dominant attractive interaction. The steric repulsion force arising from entropic loss of thermal fluctuation of DNA molecules might be a key factor to characterize the non-cross-linking aggregation.
Keywords: Bioconjugate; DNA; Gold nanoparticle; Soft interface; Synchrotron radiation SAXS;
Biofunctionalization of titanium with PEG and anti-CD34 for hemocompatibility and stimulated endothelialization by Jialong Chen; Jianjun Cao; Juan Wang; Manfred F. Maitz; Lisa Guo; Yuancong Zhao; Quanli Li; Kaiqin Xiong; Nan Huang (636-647).
Display Omitted► Hemocompatibility of the modified surface is superior to that of titanium. ► The modified surface selectively stimulates EPC adhesion. ► Unfortunately, such surface inhibits EPC proliferation. ► Denatured fibrinogen is the critical determinant of the hemocompatibility. ► Relative stability of the coating makes this technique applicable.Thrombosis and restenosis are the main causes of failure of cardiovascular and other blood-contacting biomedical devices. It is recognized that rapid endothelialization is a promising method for preventing these complications. Convincing evidence in vivo has further emerged that the vascular homing of endothelial progenitor cells (EPCs) contributes to rapid endothelial regeneration. This study deals with improving the hemocompatibility and enhancing EPC colonization of titanium by covalently bonding PEG600 or PEG4000, then end-grafting of an anti-CD34 antibody. For this, a chemically hydroxylated titanium surface was aminosilanized, which was further used for covalent grafting of polyethylene glycol and the antibody. The grafting efficiency was verified in each step. In vitro platelet adhesion analysis confirmed superior hemocompatibility of the modified surface over the control. Affinity of EPC to the surface and inhibition of smooth muscle cell adhesion, two prerequisites for endothelialization, are demonstrated in in vitro cell culture. While the coating selectively stimulates EPC adhesion, its antifouling properties prevent formation of an extracellular matrix and proliferation of the cells. Additional affinity for matrix proteins in the coating is considered for further studies. Potent inhibitory effect on macrophage activation and the relative stability of the coating render this technique applicable.
Keywords: Titanium; Hemocompatibility; Endothelial progenitor cells; Polyethylene glycol; Anti-CD34;
Can sonication enhance release from liquid-core capsules with a hydrogel membrane? by Liguo Zhang; Anne-Virginie Salsac (648-654).
Display Omitted► Sonication leads to a mass release increase proportional to its duration and ultrasonic pressure. ► At high intensities and/or long durations, sonication can lead to the capsule rupture. ► Below the breakup threshold, sonication has no remnant effect on the capsules. ► The capsules recover their physical and mechanical properties after sonication.The objective is to investigate the influence of sonication on the mechanical and release properties of hydrogel capsules. A new fabrication process is developed to fabricate millimetric capsules made of a highly-viscous liquid core protected by a thin hyperelastic alginate membrane. At high intensities and/or long exposure times, sonication can lead to the capsule rupture, because it induces fatigue in the membrane. Below the breakup threshold, no remnant effect of sonication is, however, measured on the capsule mechanical properties. The release is studied by sonicating capsules filled with blue dextran suspended in an aqueous solution. The mass release that results from sonication is found to be proportional to the sonication duration time and pressure wave amplitude. A possible physical interpretation is that the acoustic streaming flow induced by the ultrasonic wave enhances convection in the vicinity of the capsule membrane and thus mass release. We have finally quantified the passive release subsequent to low-intensity sonications: it is on average identical to the one measured on non-sonicated capsules. Overall the membrane therefore recovers its physical and mechanical properties after sonication. If sonication leads to an increase in porosity of the capsule membrane, the increase is temporary and reverses back at the end of the ultrasonic stimulation.
Keywords: Alginate capsule; Sonication; Release; Capsule breakup; Mechanical properties;
Fabrication of hierarchical structures by unconventional two-step imprinting by Gang Shi; Nan Lu; Hongbo Xu; Yandong Wang; Shoulei Shi; Hui Li; Ying Li; Lifeng Chi (655-659).
Display Omitted► A simple technique for fabricating hierarchical arrays is demonstrated. ► Nanoscale structures are fabricated with microscale stamps. ► This work provides a low-cost method to fabricate large-area hierarchical arrays.We present a simple sequential imprinting lithography method to fabricate micro/nanoscale hierarchical structures. This method involves hot embossing and capillary force lithography with two stamps of different microscales, which avoids using nanoscale stamps. By varying the experimental conditions in the capillary force lithography process, the morphology of the resulting structures can be controlled. This method may provide a facile and low-cost route for fabricating large area patterns of hierarchical structures.
Keywords: Hierarchical structure; Capillary force lithography; Microscale stamp;
The synthesis of Lewis acid ZrO2 nanoparticles and their applications in phospholipid adsorption from Jatropha oil used for biofuel by Yi-Feng Lin; Jhen-Huei Chen; Shih-Hong Hsu; Hsiang-Chi Hsiao; Tsai-Wang Chung; Kuo-Lun Tung (660-662).
Display Omitted► ZrO2 nanoparticles as a phospholipids adsorbent in Jatropha oil. ► ZrO2 nanoparticles possess higher phospholipid adsorbed capacity than commercial ZrO2 powders. ► Phospholipid removal makes Jatropha oil a potential oil for biofuel applications.ZrO2 nanoparticles were successfully fabricated via a facile hydrothermal process. The diameter and surface area of the as-prepared ZrO2 nanoparticles were approximately 5–10 nm and 102 m2/g, respectively. For the first time, Zr atoms with partial positive charges in a Lewis acid ZrO2 nanoparticle adsorbent were used for the adsorption of negatively charged phospholipids from Jatropha oil. The capacity for phospholipid adsorption using the ZrO2 nanoparticles was better than that of commercial ZrO2 powder due to the larger surface area of the ZrO2 nanoparticles. Phospholipid removal makes Jatropha oil a potential oil for biofuel applications.
Keywords: ZrO2; Adsorbent; Lewis acid; Jatropha oil; Biofuel;
Surface modification of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) by confined photo-catalytic oxidation by Ying-Chieh Yen; Chih-Chia Cheng; Yeh-Sheng Wang; Yu-Lin Chu; Chu-Hua Lu; Wantai Yang; Feng-Chih Chang (663-666).
Display Omitted► The CPO on the MEH-PPV surface results in water contact angle change without influence on optical properties. ► Water can be absorbed on the modified MEH-PPV surface without sliding even at substrate tilt angles of 90° and 180°. ► The water transport test shows that the modified MEH-PPV surface can absorb water from the pristine MEH-PPV surface. ► This is the first time that the modified π-conjugated polymer possesses the water transport behavior. ► The CPO on the MEH-PPV surface is able to further expand the use of MEH-PPV.In this study, the surface of π-conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV), was successfully modified with the sulfate anion (SO4-) groups by the confined photo-catalytic oxidation (CPO). After the surface modification, the water contact angle of MEH-PPV is changed from 95.5° to 82.1° without influence on its optical properties (based on the UV and PL spectra), and the water droplet can be absorbed on the modified MEH-PPV surface without sliding even at substrate tilt angles of 90° and 180°. The CPO on the MEH-PPV surface is able to further expand the use of MEH-PPV for applications. In addition, the water transport test indicates that the modified MEH-PPV can be a candidate for transporting water droplet.
Keywords: Confined Photo-catalytic oxidation; MEH-PPV; Water contact angle;