ordered mesoporous 
 silica ( oms ) materials have arrays of identical 
 mesopores separated by amorphous silica walls . the uniformity of the 
 mesopores and the walls is particularly attractive for a variety of 
 applications including catalysis , pharmaceutical formulation , and 
 microelectronics . oms materials are created by a supramolecular assembly process of 
 silicate molecules and surfactant . the cooperative self - assembly of 
 individual surfactant and silicate molecules is one of the proposed 
 formation mechanisms . silica precipitation on prearranged surfactant micelles , fulfilling 
 a role of liquid crystal templates , is an alternative model . after evacuation of the surfactant molecules from the assembled 
 material , mesopores separated by silica walls remain . initially , oms 
 materials were synthesized from strongly alkaline or strongly acidic 
 synthesis mixtures . particularly , ph - buffered solutions provide attractive 
 options for mastering the formation process . cok-12 is an example 
 of an ordered mesoporous silica material prepared 
 under slightly acidic , buffered conditions . the synthesis of cok-12 starts from a citric acid / citrate buffered 
 solution of amphiphilic triblock copolymer p123 ( eo20po70eo20 ) which self - assembles into spherical micelles . hydrophobic poly(propylene oxide ) ( ppo ) chains form the hydrophobic 
 core of the micelles , surrounded by a more hydrophilic layer of poly(ethylene 
 oxide ) ( peo ) chains . silica preferentially infiltrates the outer peo zone 
 of the micelles , diminishing the mobility of the peo chains and the 
 sterical stabilization of the micelle dispersion . the infiltration 
 of silica in the peo layers triggers coalescence of the original micelles 
 to form cylinders , which subsequently are arranged in a hexagonal 
 packing . in this way , its hexagonal mesostructure assembles spontaneously upon adding 
 basic sodium silicate solution to a citric acid / citrate buffered pluronic 
 p123 triblock copolymer solution . this 
 formation mechanism was investigated by identifying the intermediate 
 structures , which were prepared by limiting sodium silicate addition 
 to the buffered p123 micelle suspension ( figure 1 ) . schematic representation 
 of the different stages in the formation 
 of cok-12 , a hexagonally ordered mesoporous silica . reprinted with 
 permission from ref ( 20 ) . f127 ( eo102po70eo102 ) is 
 a related 
 triblock copolymer with substantially longer peo blocks compared to 
 p123 ( ep20po70eo20 ) . under dilute 
 aqueous conditions , f127 polymer molecules self - assemble to spherical 
 micelles with a hydrophobic core similar in size to that of spherical 
 p123 micelles but with a thicker hydrophilic palisade layer due to 
 the substantially longer peo blocks . self - assembles into micelles with a hydrodynamic radius of approximately 
 8.0 to 12 nm and a core radius of 5.9 nm . previously , f127 was used for the synthesis 
 of ordered mesoporous silica materials adopting body centered im3 m symmetry , such as sba-16 and face centered fm3m symmetry 
 in the instance of fdu-12 and kit-5 . kit-5 and fdu-12 are both synthesized 
 using f127 as a template under different synthesis conditions and 
 the use of different additives . however , the saxs diffraction patterns for both fm3m materials differ substantially due to 
 differences in pore configuration . intrigued by the documented influence of the length of the peo 
 chains in the pluronic template on the symmetry of the final silica 
 material ( cubic with f127 , versus hexagonal with p123 ) , we performed 
 synthesis experiments with f127 in citric acid / citrate buffer and 
 staged silicate addition to investigate the intermediates of this 
 oms formation process . synthesis conditions leading to formation of 
 a highly ordered new cubic phase designated as cok-19 were identified . a typical 
 buffered f127 solution was prepared 
 by dissolving 2.6 g of pluronic f127 ( basf ) in 107.5 g of deionized 
 water . to this solution , 3.684 g of citric acid monohydrate ( sigma - aldrich ) 
 and 2.540 g of trisodium citrate dihydrate ( sigma - aldrich ) were added . for the oms material synthesis , 10.4 g of sodium 
 silicate solution ( 27 wt % sio2 , extra pure , merck ) diluted 
 in 30 g of water was added to the buffered f127 solution at room temperature , 
 while stirring vigorously . precipitation of a white solid occurred 
 instantaneously , and after 5 min of stirring , the suspension was kept 
 under quiescent conditions to age for 24 h. aging was done either 
 at room temperature , 50 c , or 70 c . as - synthesized materials 
 were filtered , washed , and dried at 50 c . finally , the powders 
 were calcined in air at 350 c for 24 h using a heating rate 
 of 0.5 c min . for the investigation 
 of the assembly process with saxs , flasks 
 were filled with 3 g aliquots of buffered f127 solution . to these 
 solutions , 0.15 , 0.30 , 0.40 , 0.50 , 0.60 , 0.65 , 0.7 , 0.8 , 0.90 , and 
 1.00 ml of the diluted sodium silicate solution were added while stirring 
 vigorously . these quantities correspond to 15 , 30 , 40 , 50 , 60 , 65 , 
 70 , 80 , 90 , and 100% of the total sodium silicate amount of the typical 
 cok-19 synthesis . ph increased from 3.6 in the buffered pluronic solution to 3.8 , 4.0 , 
 4.1 , 4.3 , 4.4 , 4.5 , 4.5 , 4.7 , 4.8 , and 5.0 , respectively . dynamic light scattering ( dls ) analyses 
 of suspensions were conducted in polystyrene cuvettes at 25 c 
 on a 90plus instrument ( brookhaven instruments corporation ) , at a 
 scattering angle of 90 using a 659 nm laser . the fluctuations 
 in the scattered laser light intensity were correlated between 5 s 
 and 1 s. correlation functions were analyzed with igor pro 6.2 , using 
 the clementine package for modeling decay kinetics based on the maximum 
 entropy method . einstein 
 relation were adjusted by measuring viscosities using a rolling ball 
 viscometer ( anton paar ) . small - angle x - ray scattering ( saxs ) 
 of powder samples was recorded at room temperature using a saxsess 
 mc instrument ( anton paar ) with line - collimated cuk radiation and a 2d imaging plate detector in combination 
 with a temperature controlled rotorcell sample stage . background 
 subtraction and desmearing were performed with the saxsquant software . to investigate the formation mechanism , the scattering profiles 
 for synthesis mixtures with varying silicate concentrations were recorded 
 using a 1 mm quartz capillary flow cell sample stage mounted in the 
 saxsess mc instrument . the temperature was kept at 20 
 c using a peltier device ( anton paar , tcs 120 ) . saxs patterns 
 for the different mixtures were recorded over a time frame of 1 h. 
 ultrapure mq water was used as a background . modeling of the desmeared 
 scattering curves was performed using igor pro 6.2 in combination 
 with the ncnr sans & usans data reduction and analysis package 
 ( v7.20 ) . the recorded saxs patterns were 
 fitted with a combined model , based on spherical core synthesis mixtures containing larger amounts 
 of sodium silicate were fitted with the same model , with pseudo - voigt 
 peaks superimposed . the pseudo - voigt functions were introduced to 
 best describe the peak shapes and are a combination of lorentzian 
 and gaussian peak shapes . nitrogen 
 sorption isotherms were recorded on an autosorb-1 apparatus 
 ( quantachrome ) at 196.8 c . prior to measurement , calcined 
 samples were degassed at 150 c for 13 h under reduced pressure . nldft models 
 pore sizes are based on the nitrogen adsorption on a silica material 
 with cylindrical pores smaller than 5 nm and spherical pores larger 
 than 5 nm . scanning electron microscopy ( sem ) and scanning transmission 
 electron 
 microscopy ( stem ) images were recorded on a nova nanosem450 ( fei ) . 
 for sem , samples were dispersed on carbon tape and measured without 
 coating , using low voltages ( 0.51 kv ) to reduce sample charging . 
 in stem mode , high - resolution 
 scanning transmission electron microscopy ( hrstem ) 
 images of the cok-19 crystals were acquired using an fei tecnai g2 
 operated at an accelerating voltage of 200 kv . the images were collected 
 using a high angle annular dark field ( haadf ) detector . the samples 
 were crushed and dispersed in ethanol before a droplet of the dispersion 
 was added to a carbon coated copper grid . for electron tomography , bright field tem images was collected on an fei tecnai g2 , operated 
 at 200 kv . the tilt series of the sample aged at 70 c covered 
 angles between 72 and 76 and the series from the 
 sample aged at room temperatures 76 to 76. both 
 series were collected with a tilt increment of 2. the tomographic 
 reconstructions were performed using a sirt algorithm , and the visualization 
 was done with amira . si magic angle spinning ( mas ) 
 nmr spectra were recorded 
 using an amx300 spectrometer ( bruker ) operating at 100 mhz . the addition of sodium 
 silicate to the buffered pluronic f127 solution led to the instantaneous 
 formation of a white suspension . saxs patterns of as - made materials 
 indicated highly ordered materials ( see supporting 
 information , figure s1 ) . drying and subsequent removal of the 
 organic template by calcination resulted in porous material , coined 
 cok-19 . the calcined sample , prepared and aged at room temperature , 
 shows well resolved diffraction lines indexed in an fm3m symmetry as ( 111 ) , ( 200 ) , ( 220 ) , and ( 311 ) 
 with a unit cell parameter a = 21.9 nm ( figure 2 ) however , saxs 
 data alone are insufficient to determine meso - ordering in the structure . small 
 angle x - ray scattering patterns of cok-19 aged at room temperature , 
 50 or 70 c and calcined at 350 c . pore structure and long - range ordering were further investigated 
 using transmission electron microscopy . high angle annular dark field 
 ( haadf ) stem images reveal the structure of an ordered mesoporous 
 material consistent with the fm3m structure ( figure 3 ) . as layers of close packed spheres are forming a three - dimensional 
 structure , the layers can combine along the c direction 
 with two different sequences . abca ... stacking leads 
 to cubic close packing ( ccp ) , and aba ... stacking leads to hexagonal 
 close packing ( hcp ) . a haadf stem image 
 of a cok-19 particle aged at room temperature shows a large domain 
 of cubic ordering , with some stacking faults near the rim of the particle 
 ( figure 3a ) . an image 
 from another particle exhibited a larger amount of stacking faults , 
 suggesting some nonuniformity throughout the sample ( see supporting information , figure s2 ) . haadf - stem 
 images of cok-19 ( a ) and cok-19 - 70c crystal ( b , c ) . the cok-19 - 70c particle is rotated around the c axis 
 ( marked by a white arrow ) . the particle is viewed along [ 110]c ( b ) and [ 211]c ( c ) . fourier transforms are shown as insets in 
 a and b where streaks are characteristic for materials with stacking 
 disorder . scanning electron microscopy revealed 
 the morphology of the calcined 
 cok-19 as aggregates of truncated octahedrons with a mean diameter 
 of approximately 500 nm to 3 m ( figure 4 ) . si mas nmr analysis of the 
 as - synthesized cok-19 material was performed to analyze the degree 
 of condensation ( see supporting information , figure s8 ) . q represents q , q , and q signals at 92 , 
 101 , and 110 ppm respectively , with an intensity distribution 
 of 9% , 42% , and 48% , indicating a condensed silicate network even 
 at room temperature . freshly synthesized cok-19 suspensions were aged at 50 and 
 70 c 
 instead of room temperature for 24 h. low angle diffractograms of 
 calcined cok-19 materials aged at 50 and 70 c resulted in less 
 ordered material and caused the unit cell to increase to 25.9 and 
 27.2 nm , respectively ( figure 2 ) . the structure loss was also apparent from haadf images 
 for cok-19 - 70c , aged postsynthesis at 70 c ( figure 3b ) . this material has more 
 stacking faults , which gives rise to streaks in the fourier transform 
 of the image . tem is a method to study the local structure of selected 
 particles . by combining the information from tem with the results 
 from saxs , which provide averaged information from the entire sample , 
 it can be confirmed that the sample aged at room temperature possesses 
 a higher quality cubic ordering , with stacking faults increasing with 
 temperature . heating causes considerable swelling of pluronic 
 micelles . aging above 
 room temperature 
 of the cok-19 aggregates formed at room temperature introduced stacking 
 faults in the material . the introduction of stacking disorders upon 
 heating suggests that , in the initial colloids , the interaction between 
 pluronic core silica shell particles is still largely physical , 
 enabling alteration of stacking . besides line broadening through 
 general lattice disorder , stacking 
 faults in the c direction also affect the saxs pattern . hcp intergrowths in a ccp structure influence line width and positions 
 of certain reflections . these stacking disorders , 
 also known as intergrowths , occur more frequently for cok-19 - 70c as 
 was seen with haadf - stem . cok-19 - 70c was aged at higher temperatures , 
 where energetic differences between hcp and ccp packings become less 
 deterministic . the increasing fraction of stacking disorder with temperature 
 also explains the decreasing resolution of the low angle reflections 
 in the saxs curve with increasing aging temperature ( figure 2 ) . cok-19 displayed a nitrogen physisorption isotherm with characteristics 
 of both micro- and mesopores ( figure 5a , table 1 ) . the cage diameter is 7.0 nm , and the mesopore volume is 
 0.09 cm g. the total pore volume of 
 0.29 cm g is mostly microporous ( 0.2 
 cm g ) . adsorption (  ) 
 and desorption (  ) branches of nitrogen 
 physisorption isotherms of calcined ( a ) cok-19 , ( b ) cok-19 - 50c , and 
 ( c ) cok-19 - 70c . pore diameter based on the nldft 
 analysis for adsorption or as represented in the references . wall thickness is determined based 
 on pore diameter and unit cell parameter of a fm3m structured material : wt = 
 ( a/2 )  dp . volume of micropores and small mesopore , 
 calculated using the t - plot method ( see the supporting 
 information figure s9 ) . micropore volume including the 
 volume of the interconnecting pores , if the latter are of a diameter 
 below 4 nm . increasing the aging temperature to 50 c resulted 
 in a larger 
 hysteresis loop ( figure 5b ) . the cok-19 - 50c material has a mesopore size of 9.4 nm and a mesopore 
 volume of 0.32 cm g. such a temperature 
 induced increase of mesopore diameter and volume is commonly observed 
 in pluronic based synthesis and has been ascribed to an increased 
 hydrophobicity of the eo moieties , expanding the size of the micellar 
 core . cok-19 - 50c contains a volume of 0.46 cm g of smaller mesopores ( 2.5 nm ) and almost no micropores , 
 resulting in a total pore volume of 0.78 cm g ( table 1 ) . the significant 
 increase of pore volume compared to the sample aged at room temperature 
 and the presence of small mesopores can be interpreted as follows . owing to the swelling of the individual micelles , upon stacking some 
 spaces are left between the core incrementing the aging temperature further to 70 c 
 increased 
 the mesopore size to 11.2 nm and the mesopore volume to 0.63 cm g. the size of the small mesopores was 
 also increased to 3.2 nm . from the pore size distribution ( table 1 ) and the unit cell 
 parameter a derived from saxs , the wall thickness 
 was estimated to be approximately 
 89 nm for all materials , aged at different temperatures . these 
 large wall thicknesses , together with a high degree of silica condensation , 
 according to si nmr , are expected to contribute high 
 mechanical stability to these materials . in order to investigate the pore structure of the material 
 in more 
 detail , electron tomography was performed on the sample aged at room 
 temperature as well as at 70 c ( cok-19 - 70c ) . from the tomographic 
 reconstructions , an arrangement of the pores consistent with the proposed 
 structure model can be resolved in 3d ( figure 6 , figures s3s7 and a rotating 3d 
 representation in the supporting information ) . the mesopores in the sample aged at room temperature are smaller 
 and more separated by pore walls compared to the pores in the sample 
 aged at 70 c . tomography shows the cok-19 material has isolated 
 spherical mesopores , separated by a thick silica wall , whereas the 
 material aged at 70 c shows some of these mesopores are interconnected . moreover , these mesopores are stacked in a cubic order . when temperature 
 is increased during the aging process , pore sizes increase and stacking 
 is less ordered , causing some of these pores to connect . pore structure of cok-19 ( a , c ) and cok-19 - 70c ( b , d ) revealed 
 by orthoslices through the electron tomography reconstructions , a 
 and b , and as segmentations of the pores , shown in purple , c and d. 
 all four views are along a   direction , and the arrangement of 
 pores is consistent with cubic close packing . in cok-19 , the pores 
 are well separated , whereas in the cok-19 - 70c sample some of the pores 
 are interconnected . table 1 gives an 
 overview of fm3m ordered 
 mesoporous materials reported in literature , synthesized using f127 
 ( kit-5 and fdu-12 ) or other amphiphilic surfactant templates such 
 as brij76 ( sba-12 ) and b-506600 ( fdu-1 ) . cok-19 is crystallized 
 in circum neutral conditions , while the materials from literature 
 are typically synthesized in hydrochloric acid environment . the materials 
 from literature have been reported to be intergrown structures , combining 
 cubic with hexagonal symmetry , similar to the cok-19 - 50c 
 and 70c . aging at increased temperature not only increases 
 the fraction of stacking disorders , it also dramatically increases 
 the overall porosity . the total porous volume of cok-19 is in the 
 range of 0.29 to 0.88 cm g , of which 
 up to 0.46 cm g can be located in 
 the micropores and small mesopores . among all of the reported mesoporous 
 silica materials , fdu-12 is the only one exhibiting similar wall thicknesses , 
 although the unit cell dimensions and pore sizes are approximately 
 the double of cok-19 as a result of swelling agents used in the synthesis . 
 besides these fm3m type materials 
 synthesized using amphiphilic surfactants , also cationic surfactants 
 have been used . for a deeper understanding of the 
 material and its properties , the formation process of this material 
 was investigated by dls and saxs characterization of intermediates 
 in the cok-19 synthesis . a series of samples was prepared by adding incremental amounts of 
 sodium silicate solution to buffered f127 solution . at silicate additions 
 of less than 70% of the nominal quantity , the synthesis mixture was 
 optically transparent , while at higher silicate contents the mixture 
 became turbid ( figure 7 ) . at 70% silica addition a viscous gel was obtained , and eventually 
 at 90% and 100% silica addition a suspension of particles was obtained . 
 in figure 7 , the onset 
 of sedimentation is already visible in the sample containing the total 
 silica amount . photograph of the series of synthesis mixtures containing 
 citrate 
 buffered f127 surfactant solution and 0% , 15% , 30% , 40% , 50% , 60% , 
 65% , 70% , 80% , 90% , and 100% of silica addition . buffered solution , pluronic f127 formed micelles 
 with a hydrodynamic radius of 6.6 nm . it is commonly known that triblock 
 copolymers such as p123 and f127 form spherical micelles in dilute 
 aqueous solutions . these micelles are 
 composed of a dense core of hydrophobic ppo moieties , which are sterically 
 stabilized by a diffuse shell of peo chains . when up to 50% of the total silica amount is added to the buffered 
 f127 solution , the radius of the particles increases slightly with 
 a few nanometers ( table 2 , figure s10 ) . scanning transmission electron microscopy ( stem ) of an evaporated 
 synthesis mixture with 50% silicate addition confirmed the formation 
 of spherical nanoparticles . the bright field stem micrograph ( figure 8) shows loosely aggregated , 
 monodisperse spherical nanoparticles with radii of ca . increasing 
 the silica concentration further led to a further increase in particle 
 size . however , dls was limited to samples with 65% of the total silica 
 amount . higher silica amounts led to a sharp transition of more aggregated 
 particles , which could not be monitored with dls . using saxs , these 
 nanostructures could be analyzed by modeling the scattering patterns 
 with spherical core shell models , giving additional information 
 on shape , inner structure , and aggregation state . bright field stem image 
 of f127 micelles , to which only 50% of 
 the nominal silicate quantity was added . in the initial buffered f127 solution , the scattering contrast 
 between the aqueous environment and the f127 micelles was insufficient 
 to enable recording a saxs pattern . saxs patterns of synthesis mixtures 
 with 15% up to 100% of the nominal silicate content are presented 
 in figure 9 . at silicate 
 contents below 65% , the scattering curves could be described by a 
 spherical core  shell model , in which the electron density of 
 the core was lower than in the shell ( details provided in the supporting information ) . these differences in 
 contrast were interpreted as a core consisting of organics surrounded 
 by a shell containing silica . regarding contrast , it is noteworthy 
 that due to dilution in an aqueous solution , the presence of the organic 
 f127 surfactant inside the pores , and an incomplete silica condensation 
 in the final material , scattering contrast is suboptimal . after filtration 
 and removal of the organic template through calcination , diffraction 
 lines in the saxs pattern are sharper and more pronounced ( figure 2 ) . saxs patterns of synthesis 
 mixtures consisting of buffered f127 
 surfactant solutions to which an increasing amount of sodium silicate 
 was added : ( a ) 15% , ( b ) 30% , ( c ) 40% , ( d ) 50% , ( e ) 60% , ( f ) 65% , ( g ) 
 70% , ( h ) 80% , ( i ) 90% , and ( j ) 100% of the standard synthesis . on analogy with previously investigated p123 micelles , the organic core is interpreted as the ppo part 
 of the f127 micelle , while the shell consists of the peo chains and 
 infiltrated silica . an overview of estimated core radii and shell 
 thicknesses depending on silica addition is presented in table 2 . the overall particle 
 radii for core  shell particles , with increasing sodium silicate 
 content , were consistent with the size estimation from dls . this discrepancy 
 is caused by the presence of a solvation layer , reducing the diffusivity 
 and increasing the size of particles in dls measurements . saxs 
 patterns and model fittings are shown in figures 9 and 10 and figures 
 s11s21 in the supporting 
 information . the high q part of the residual 
 ( q values > 0.2 a ) additionally 
 displayed the fingerprint of subnanometer particles . shell micelle description 
 led to a size estimation of nanoparticles of approximately 0.6 nm . previously , similarly sized silica nanoparticles have been observed 
 in saxs studies of zeolite formation processes and have been identified 
 as partially condensed silicate oligomer aggregates from which crystallization 
 originates . in the present system , it seems these silicate oligomers are the 
 micelle infiltrating species . this interpretation was supported by 
 the observation that the scattering intensity at q values > 0.2 a assigned to silica nanoparticles 
 did not change with increasing silica content . silica nanoparticles 
 formed in solution infiltrate the peo fuzzy layer of f127 micelles 
 and precipitate forming a capsule . similar spherical silica infiltrated 
 micelles were observed using p123 triblock copolymer in the formation 
 of hexagonally ordered mesoporous silica materials . as silica is added , more silica is concentrated in the hydrophilic 
 peo layer , increasing the shell thickness , slightly compressing the 
 ppo core ( table 1 ) . saxs 
 patterns of f127 surfactant solutions to which ( a ) 15% , ( b ) 
 40% , ( c ) 60% , ( d ) 70% , ( e ) 80% , and ( f ) 100% of the total sodium silicate 
 amount in a standard synthesis was added and corresponding fitting 
 with core  shell micelle model and unassociated silica nanoparticles . patterns a , b , and c were fitted with a combined model for polydisperse 
 core  shell particles and smaller , dense spherical particles . patterns d , e , and f were fitted with the same model superimposed 
 with pseudo - voigt peaks ( supplementary modeling information can be 
 found in the supporting information ) . the addition of 70% and higher 
 percentages of the silica caused 
 spontaneous aggregation of the silica coated f127 micelles . in saxs , 
 a structuring factor appeared in the small angle scattering patterns , 
 which was modeled using pseudo - voigt peaks . the introduction of pseudo - voigt 
 peaks in the model corresponds to the appearance of bragg diffraction . suspensions with 80% up to 100% silicate addition required three pseudo - voigt 
 peaks to adequately describe the saxs patterns . the scattering intensity 
 at q values > 0.2 a remained 
 constant , whereas , relatively , the amount of scattering from core  shell 
 particles decreased . shell 
 micellar structures in the assembly process . from this series 
 of saxs experiments and the previously illustrated 
 cok-12 formation mechanism , the following 
 formation mechanism is proposed ( figure 11 ) . when the highly alkaline sodium silicate 
 solution is added to the citrate buffered f127 solution , silicate 
 anions are protonated and form neutral silicate oligomers and orthosilicic 
 acid si(oh)4 . the silicate oligomers interact strongly 
 with the peo tails of the pluronic micelles , condensing in between 
 the diffuse layer of peo chains . schematic representation of cok-19 formation mechanism , 
 showing 
 the effect of increased silica concentration . silica ( blue ) is precipitated 
 on the peo chains of the pluronic f127 micelles ( brown ) . the silica 
 layer around the f127 micelles will increase in thickness until sterical 
 stabilization is overcome and spherical silica coated micelles start 
 to aggregate , ultimately stacking in a cubically ordered structure . the synthesis was performed at 
 ph 5 , close to the isoelectric point 
 of f127 . the absence of charge , together with the large salt concentration , 
 implies stabilization of the f127 micelles must occur through sterical 
 effects of the peo chains . with increasing sodium silicate concentration , 
 larger amounts of silica are incorporated in the peo layer , increasing 
 the shell thickness around the micelles . it is interesting to note 
 that in the cok-12 formation , sterical stabilization was overcome 
 after adding only 15% of the nominal silica amount , transforming the 
 coated , spherical micelles into elongated cylinders . in contrast , 
 the silica coated pluronic f127 micelles omit to form a cylindrical 
 intermediate and form a regular arrangement of close packed silica 
 coated spheres . as the main difference between both syntheses is the 
 length of the peo chains of the pluronic surfactants ( eo20 versus eo102 for , respectively , p123 and f127 ) , the difference 
 in sterical stabilization and consequently the different self - assembly 
 process must be attributed to the increasing chain length . by replacing the p123 pluronic with the f127 as a template in the 
 formation of mesoporous silica , a new ordered material was discovered . this cok-19 material has a fm3m symmetry with hcp intergrowths , which increase with increasing temperature . the material contains spherical mesopores of 711 nm , interconnected 
 via micropores and small mesopores in its 89-nm - thick silica 
 walls , which could be tuned via varying aging temperature . intermediates 
 in the formation process of the cok-19 material could 
 be investigated by limiting the silicon source and modeling the saxs 
 pattern . uncharged f127 micelles are wrapped with silica by accumulation 
 of the silicate oligomers in the hydrophilic peo layer of the micelles . silica shell particles self - assemble in a cubic 
 close packed organization , ultimately forming the cok-19 material .
a new ordered mesoporous silica material 
 ( cok-19 ) with cubic symmetry 
 is synthesized by silicate polycondensation in a citric acid / citrate 
 buffered micellar solution of pluronic f127 triblock copolymer near 
 neutral ph . 
 saxs , nitrogen adsorption , tem , and electron tomography 
 reveal the final material has a cubic close packed symmetry ( fm3m ) with isolated spherical mesopores 
 interconnected through micropores . 
 heating of the synthesis medium 
 from room temperature to 70 c results in a mesopore size increase 
 from 7.0 to 11.2 nm . 
 stepwise addition of the silicate source allows 
 isolation of a sequence of intermediates that upon characterization 
 with small - angle x - ray scattering uncovers the formation process via 
 formation and aggregation of individual silica - covered pluronic micelles .