the spontaneous formation of organized 
 patterns as an intrinsic 
 property of a system containing discrete constituents , a process termed 
 self - assembly , has fascinated scientist in all 
 fields because entropy commonly leads to disorder . nature displays 
 the enormous potential of self - organization attributed to many of 
 the unexcelled properties of biological matter ; for example , self - repair 
 originates from the ability to achieve self - assembly . in materials science , full exploration of this potential 
 has still not been achieved , and for the next level , which is programmable 
 self - assembly , we need to learn how to encode more complex interaction . 
 for nanoparticles , one learns that a straightforward approach for 
 finding unique self - assembled structures is to implement long - range 
 and highly directional repulsive forces in addition to the attractive 
 interactions , which are responsible for aggregation first . a 
 special class of self - assembled materials is given by liquid 
 crystals . these special features lead to a plethora of fascinating properties 
 as also stated in the seminal article published by tschierke in 2013 . liquid crystals are formed by unique molecular 
 compounds , and one can roughly distinguish between thermotropic and 
 lyotropic liquid crystals ( llcs ) . llcs and , at lower concentration , 
 micellization rely on amphiphiles , most importantly surfactants . surfactants 
 are low - molecular - weight compounds comprising a hydrophilic headgroup , 
 often charged , attached to at least one alkyl - chain of medium length 
 ( c12c20 ) as a hydrophobic entity . an 
 important variable in surfactant science is the so - called packing 
 parameter , a number describing roughly the shape of the molecule . on programmed self - assembly in the sense discussed above , there exists 
 a substantial limitation : intermolecular interactions can not be tuned 
 without substantially changing the morphology and solvent compatibilities 
 of the surfactant at the same time . for instance , although the role 
 of the charge of the headgroup has been discussed intensely for classical , organic surfactants , one can hardly extend the charge 
 to values larger than 2 without significantly altering the packing 
 parameter . what one can do is to increase the number of charged functionalities , 
 but an additional headgroup will of course alter the molecular shape 
 significantly . therefore , for any effect , it would be unclear if this 
 is due to the charge , the altered packing parameter , or both . , 
 we will report about the synthesis of such surfactants 
 with highly charged head , and we will investigate the self - assembled 
 structures formed at different concentrations in water . thus , one could 
 imagine obtaining differently charged surfactants without changing 
 their shape , when such transition - metal containing entities are used 
 as head groups . however , an important 
 question is , which kind of  inorganic moiety  is most 
 suitable for our purpose . recently , we presented a prototype for hybrid 
 surfactants ( denoted as pw11c16 ) containing 
 a polyoxometalate ( pom ) headgroup [ pw11o39 ] . it was synthesized starting from a so - called lacunary keggin ion 
 [ pw11o39 ] ( see also figure 1 ) . because lacunary compounds exist not only for phosphorus 
 but also for other elements e in the center of the oxo - cluster ( e 
 = si(iv ) , b(iii ) ) , our idea is to prepare 
 a systematic series of surfactants with identical structure but different 
 overall charge and to examine the effect of the increasing charge 
 on self - assembly . the lacunary polyoxometalates k7[pw11o39 ] , k8[siw11o39 ] , and 
 k8h[bw11o39 ] were synthesized according to the literature . in a 5 l beaker , 5.00 
 g of powdered k7[pw11o39]14 
 h2o ( 1.56 mmol ) was dissolved in 5 l of acetonitrile . to 
 the resulting suspension , 3.67 mmol of hexadecyltrimethoxysilane , 
 4.4 eq of 1 m hcl ( 7.34 ml ) , and 7.5 eq of tetramethylammonium chloride 
 were added and stirred for 24 h at room temperature . after filtration 
 and removal of the solvent , the resulting white precipitate was collected 
 and washed with water , methanol , and diethyl ether ( 50 ml each ) . h nmr ( dmso - d6 ) :  
 = 3.23 ( s , 36h ) , 1.621.08 ( m , 56h ) , 0.85 ( t , j = 6.7 , 6h ) , 0.71 ( t , j = 7.5 , 4h ) . si nmr ( dmso - d6 ) :  = 51.20 . w - nmr ( 25 mhz , acetonitrile - d3 ) : 
  = 103.16 ( d , j = 1.0 hz , 2w ) , 108.71 
 ( d , j = 1.0 hz , 2w ) , 112.78 ( d , j = 1.5 hz , 1w ) , 124.63 ( d , j = 1.2 hz , 2w ) , 
 202.35 ( d , j = 1.6 hz , 2w ) , 253.96 
 ( d , j = 1.4 hz , 2w ) . ir ( atr ) : 1111 ( si  o  si ) , 
 1063 ( p  o ) , 1051 ( p  o ) , 1033 ( p  o ) , 981 , ( w = 
 o ) , 959 ( sh , w = o ) , 951 ( w = o ) , 861 ( w  o  w ) , 810 ( w  o  w ) , 
 776 ( w  o  w ) , 747 ( w  o  w ) , 704 ( w  o  w ) . elemental analysis c , h , n : 15.47% , 3.1% , 1.23% . in a 5 l beaker 5.00 
 g of powdered k8[-siw11o39]13 h2o ( 1.56 mmol ) was dissolved in 5 l of acetonitrile . 
 to the resulting suspension , 3.67 mmol of hexadecyltrimethoxysilane , 
 4.4 eq of 1 m hcl ( 7.34 ml ) , and 7.5 eq of tetramethylammonium chloride 
 were added and stirred for 24 h at room temperature . after filtration 
 and removal of the solvent , the resulting white precipitate was collected 
 and washed with water , methanol , and diethyl ether ( 50 ml each ) . yield : 
 4.57 g ( 84% based on k8[-siw11o39 ] ) , white powder . h nmr ( dmso - d6 ) :  = 3.23 
 ( s , 48h ) , 1.621.08 ( m , 56h ) , 0.86 ( t , j = 
 6.7 , 6h ) , 0.56 ( t , j = 7.5 , 4h ) . w - nmr ( 25 mhz , acetonitrile - d3 ) :  = 112.77 ( 2w ) , 116.69 
 ( 2w ) , 119.91 ( 1w ) , 133.43 ( 2w ) , 180.09 ( 2w ) , 
 257.37 ( 2w ) . elemental analysis c , h , n : 16.50% , 3.29% , 1.60% . in a 5 l beaker , 5.00 
 g of powdered k8h[-bw11o39]13 h2o ( 1.56 mmol ) was dissolved in 5 l of acetonitrile . 
 to the resulting suspension , 3.67 mmol of hexadecyltrimethoxysilane , 
 4.4 eq of 1 m hcl ( 7.34 ml ) , and 7.5 eq of tetramethylammonium chloride 
 were added and stirred for 24 h at room temperature . after filtration 
 and removal of the solvent , the resulting white precipitate was collected 
 and washed with water , methanol , and diethyl ether ( 50 ml each ) . yield : 
 4.2 g ( 76% based on k8h[-bw11o39 ] ) , white powder . h nmr ( dmso - d6 ) :  = 3.23 
 ( s , 51h ) , 1.621.08 ( m , 56h ) , 0.85 ( t , j = 
 6.7 , 6h ) , 0.62 ( t , j = 7.5 , 4h ) . cations 
 were exchanged to na by slow filtration of a 
 5 mg / ml solution of tma - pom through a column packed with amberlite - ir120-h / na . complete exchange was confirmed via h nmr ( absence of 
 signal at  = 3.23 ppm ) . nmr measurements ( h , b , c , si , p ) were 
 performed on a varian unity inova 400 spectrometer . the w - nmr - spectra were recorded on a bruker avance iii 600 mhz spectrometer 
 with 10 mm nmr tubes . saxs was acquired on a bruker nanostar system equipped with 
 pinhole collimation and cu k radiation . the samples were placed 
 between x - ray transparent mylar foils and were measured in an evacuated 
 chamber . for avoiding the contamination of the measurement chamber , 
 samples were dried prior to use . liquid samples were sealed in a 1 
 mm mark - tubes made of soda lime glass . modeling of liquid cell data 
 was performed using the sasview software ( developed by the danse project 
 under nsf award dmr-0520547 ) . textures of liquid - crystalline samples 
 were studies with an olympus cx41 light microscope . the dry sample 
 was placed directly on carbon - coated copper grids . for cryo transmission 
 electron microscopy studies , a sample droplet of 2ul was put on a 
 lacey carbon filmed copper grid ( science services , muenchen ) , which 
 was hydrophilized by air plasma glow discharge unit ( 30s with 50w , 
 solarus 950 , gatan , muenchen , germany ) . subsequently , most of the 
 liquid was removed with blotting paper in a leica em gp ( wetzlar , 
 germany ) grid plunge device , leaving a thin film stretched over the 
 lace holes in the saturated water atmosphere of the environmental 
 chamber . the specimens were instantly shock frozen by rapid immersion 
 into liquid ethane cooled to approximately 97k by liquid nitrogen 
 in the temperature - controlled freezing unit of the leica em gp . the 
 temperature was monitored and kept constant in the chamber during 
 all the sample preparation steps . the specimen was inserted into a 
 cryotransfer holder ( ct3500 , gatan , muenchen , germany ) and transferred 
 to a zeiss / leo em922 omega eftem ( zeiss microscopy gmbh , jena , germany ) . zero - loss filtered 
 images ( e = 0 ev ) were taken under reduced 
 dose conditions ( 1001000 e / nm ) . all images were 
 registered digitally by a bottom mounted ccd camera system ( ultrascan 
 1000 , gatan , muenchen , germany ) combined and processed with a digital 
 imaging processing system ( digital micrograph gms 1.9 , gatan , muenchen , 
 germany ) . collected images were processed with a background - subtraction 
 routine , and where appropriate , a smoothing filter ( butterworth filter ) 
 was applied to reduce noise . based on our work on surfactants with a [ pw11o39 ] head , the main aim of the current work 
 is to increase the charge of the head by synthesizing new surfactants 
 containing [ siw11o39 ] and 
 [ bw11o39 ] moieties . because 
 only the central element is varied , we expect that only charge differs 
 and molecular shape remains constant . the latter was one of the key 
 goals formulated in the introduction section 
 of this paper . three surfactants ew11c16 were prepared by condensation of two alkylsilanes to the cavity 
 of the lacunary species [ ew11o39 ] ( n = 3,4,5 ) . the resulting 
 compounds were characterized unambiguously by a combination of analytical 
 methods , most importantly electro - spray ionization mass spectrometry 
 ( esims ) recorded in anion mode shown in figure 1 . for overview spectra , 
 see supporting information , figures s-1 to s-3 . one can identify several signals , which correspond to either the 
 molecular ion or fragments having different charge due to attachment 
 of cations ( most importantly h ) . the signals for the bare 
 ions [ ew11o40si2c32h66 ] ( ne = p = 3 ; ne = si = 4 ; ne = b = 5 ) are present , but they are relatively 
 weak in intensity . instead , the most intense signal was selected for 
 detailed analysis in each of the cases ( figure 1 ) . by comparison to theoretically modeled 
 patterns , we see there is an agreement with the triply charged , partially 
 protonated species . please note that in such spectra , mass is divided 
 by charge z. thus , a signal at 1066.74 g mol ( average m / z ) for 
 a charge of 3 represents a species with m = 3200.22 g mol ( pw11c16 ) . a distance 
 of 1/3 between each isotope peak as for the signals shown in figure 1 indicates a charge 
 of 3 . supporting information figures 
 s-1 , s-2 , s-3 summarize all additional spectroscopic data for pw11c16 , siw11c16 , and bw11c16 . siw11c16 will be discussed 
 here as an exemplary case : in si nmr ( figure s-2a , b ) , one observes two signals characteristic for 
 the silicon atom in the center of the oxo - cluster (  = 85 
 ppm ) and the one attached to the hydrocarbon chain (  = 52 
 ppm ) . additionally , coupling between silicon and the different w atoms 
 of the pom - cluster can be seen ( jsi  w = 10.3 hz , 21.1 hz ) . the structure of the headgroup 
 proposed in figure 1 could also be proven by the characteristic 2:2:1:2:2:2 pattern and 
 the jw w = 1020 
 hz coupling constant in w - nmr spectra ( figure s-2c ) . the observation of the mentioned nuclear coupling 
 shows that the nmr experiments have been performed with high sensitivity . 
 because no unwanted signals are seen , we assume that there are no 
 impurities present within the detection limit of nmr spectroscopy . elemental analysis was aggravated by difficulties in drying / quantitative 
 removal of any solvents used during synthesis ( e.g. , water ) . however , 
 chn values are in satisfactory agreement ( e.g. , for tma4[siw11o40(sic16h33)2 ] ; c : 16.50% ( calcd 16.31% ) , h : 3.29% ( calcd 3.49% ) , n : 1.60% 
 ( calcd 1.78% ) ) ; see also the experimental section . top : reaction sequence for the synthesis of surfactants with different 
 heteropolytungstate head groups and systematically varying charge . middle : molecular structure of 
 the resulting surfactant ( hydrogen atoms omitted ) with the headgroup 
 region highlighted in polyhedral plot ( green  wo6 octahedra ; gray  eo4 tetrahedron ) . right : main 
 signals in esims patterns for the compounds with different central 
 atoms . p : blue graph  experimental pattern ; pale blue bars 
  simulated pattern for [ c32h66si2pw11o40 ] . si : black 
 graph  experimental pattern ; gray bars  simulated 
 pattern for h[c32h66si3w11 o40 ] . b : red graph  experimental 
 pattern ; pale red graph  simulated pattern for h2[c32h66si2bw11o40 ] . magnified images of the above signals are 
 given in the supporting information figures 
 s-1 , s-2 , s-3 . h nmr , ft - raman , 
 and ft - ir spectra ( figure s-2d , f ) are also 
 in full agreement with the proposed 
 structure of siw11c16 . please note that cation 
 exchange ( na , h ) is necessary for increasing 
 the solubility of the surfactants in water compared to the organic 
 ( ch3)4n counterion originating from 
 the first synthesis step ( see figure 1 ) . the solubility with tetramethylammonium as a cation 
 is less than 1 mg / ml . after cation exchange ( e.g. for na ) solubility increases and is of the order of 100 mg / ml . from spectroscopic 
 data ( see supporting information figures 
 s-1 , s-2 ) , one can conclude the cation exchange does not affect the 
 integrity of the molecular structure of the surfactants at all . after 
 successful preparation and characterization of the ew11c16 compounds , it is time to explore their amphiphilic 
 features with special emphasis on self - organized structures and the 
 dependency on headgroup charge . a dispersion containing c0 = 75% weight surfactant was used for the sample preparation 
 ( see also the experimental section ) . agreeing 
 with our previous results on this system , the na - pw11c16 surfactant forms phases which 
 are typical for lyotropic liquid crystals . the llc character can be 
 seen from birefringence in optical microscopy between crossed polarizers 
 ( polmic ) ( see figure 2a ) . the so - called smokey / mosaic texture is in agreement with a hexagonal 
 phase . in transmission electron microscopy ( tem ) images taken from 
 dried samples , one can observe a nicely ordered structure comprising 
 cylindrical aggregates arranged in a hexagonal packing p6/mm ( figure 2b ) , which is a common llc phase . results from small - angle 
 x - ray scattering ( saxs ) shown in figure 2c confirms the latter . the periodicity of 
 the hexagonal system is a = 4.2 nm ( q = 1.49 nm ) . if we consider that the extension 
 of a single surfactant is roughly 3.0 nm , one has to assume there 
 is partial interdigitation of the alkyl chains in the cylindrical 
 aggregates , which is also not unusual in llc phases . polmic ( a ) , tem ( b ; scale 
 bar 100 nm ) and saxs ( c ) data for the 
 na - pw11c16 surfactant at high concentration . polmic ( d ) , tem ( e ; scale bar 100 nm , inlet : scale bar 10 nm ) and 
 solid - state saxs ( f ) data for the na - siw11c16 surfactant at high concentration . black bars mark the expected patterns 
 for a cylindrical - hexagonal phase p6/mm ( c ) and a lamellar phase im3 m ( f ) , 
 and the inset graphics show the suiting llc phase . next , we want to discuss siw11c16 used at 
 otherwise constant conditions ( c0 = 75% 
 weight ; na as a counterion ) . the headgroup charge of the 
 surfactant has increased to 4  . a first assessment  if 
 the change in headgroup charge has an influence  can be done 
 using polmic ( figure 2d ) . this is in agreement with saxs 
 measurements ( figure 2f ) pointing to a lamellar substructure with a periodicity of 6.6 
 nm ( q = 0.94 nm ) . the mentioned 
 periodicity is substantially larger than for na - pw11c16 and is of the order of twice the extension of a single surfactant , 
 which is quite typical for lamellar surfactant structures . unfortunately , 
 the signals of the lamellar phase are relatively week and are superposed 
 by an unspecific tail , which might indicate there is also a less structured , 
 amorphous part of the sample . tem measurements ( figure 2e ) reveal that na - pw11c16 does not form a common lamellar phase with sheets extended in 2-d . the structure is unique : objects with stripy , periodic features ( a = 6.5 nm ) are identified , which are extended in one direction 
 up to 150 nm ( figure 2e ) . however , we recognize several unusual features . for a lamellar 
 phase it is unusual that confined rod - like growth is favored over 
 extended 2-d growth , for example , into sheet - like structures . one 
 should also note the extension of the self - organized aggregates perpendicular 
 to the growth axis is fairly uniform ( 10 nm ) . because of the 
 large difference in electron density between the w - containing head 
 and the hydrocarbon side chains , one can easily differentiate between 
 inorganic ( dark ) and organic ( bright ) regions in the structure . considering 
 the dimensions of the respective region , one can then speculate about 
 how the surfactant is organized in the self - assembled structure . the 
 size of the dark stripes is 2 nm , according to evaluation 
 of tem data using the program imagej . for better visibility , a high - resolution 
 image was added as an inset in figure 2e . force - field calculations were done , pointing out 
 that the extension of the head [ siw11o39 ] headgroup 
 with attached counterions is roughly 1 nm . thus , we assume 
 a double - layer packing of the surfactants in the structure ( see also scheme 1 ) . because the cations 
 ( shown 
 in blue ) can not penetrate into the alkyl - phase ( black ) , there is shielding 
 of the field predominantly in one direction . balance of repulsion 
 with attractive forces ( black vectors ) determines the formation of 
 the particular self - assembled structures . regarding the structure 
 of the self - assembled aggregates of siw11c16 ( a ) at high concentration , see also figure 2e , and at low concentration ( dumbbell aggregates ) , 
 see also figure 3d , e . ( b ) regarding the behavior for the lower - charged pw11c16 surfactant , see figure 2b for hexagonal llc phases and figure 3c for classical micelles in water . the size of the bright stripes ( 4.5 nm ) compared 
 to the 
 length of the alkyl - chains ( lchain  
 2.2 nm ) provides evidence for a stretched conformation and the absence 
 of any interdigitation . if the alkyl - chains would interpenetrate or 
 were strongly bent , a significantly smaller value for the alkyl - region 
 would have been expected . similar patterns , as seen in figure 2e , have been reported in the 
 past for nanoparticles , for example , prismatic bacro4 , forming ordered chains induced by oriented attachment . considering the various arguments , we propose 
 the structure for the aggregates shown in scheme 1a . plate - like aggregates with a bilayer substructure 
 stack , resulting in the  striped worms  and the overall 
 lamellar architecture . the charge of the na - bw11c16 surfactant is even one unit higher ( see figure 1 ) , and this seems to prevent any defined 
 self - organization , at least under conditions chosen here . in polmic 
 ( given in supporting information figure s-4a ) one sees birefringent , fractal objects , that look similar to phases 
 found for columnar thermotropic liquid crystals . however , in tem ( figure s-4b ) and saxs ( figure s-4c ) , no particular structure is observed . only seldom , and 
 not very reproducibly , a spot with an unusual structure comprising 
 triangular shapes ( figure s-4d ) is found . because of the lacking ability of bw11c16 to 
 present well - defined llc systems , we did not consider it for further 
 studies . for 
 conventional surfactants we expect that in water , at lower concentrations 
 ( c = 10 mg / ml ) compared to the llc phases but above 
 a critical concentration ( cmc ) , micellar aggregates will be observed . this is exactly the case for h - pw11c16 , as shown 
 in figure 3a , c . particle size distributions derived from dynamic 
 light scattering measurements ( dls ) show species with a hydrodynamic 
 radius of 2.4 nm , which fits well to spherical micelles composed of 
 partially interdigitated surfactant molecules . all aggregates have a dark rim , which we 
 assign to the high electron density of the [ pw11o39 ] head and the resulting imaging contrast . dls measurements of aqueous dispersions 
 ( c = 10 
 mg / ml ) of the h - pw11c16 surfactant ( a ) and of 
 the h - siw11c16 surfactant ( b ) . tem micrograph 
 of a h - pw11c16 micellar dispersion ( c ) and of 
 aggregates formed by h - siw11c16 in water at 
 two different magnifications ; scale bar = 50 nm ( d ) , scale bar = 25 
 nm ( e ) . ( f ) saxs data recorded from aqueous dispersions of h - pw11c16 ( blue circles ) , fitted using a spherical core  shell 
 model ( blue line ) and h - siw11c16 ( black squares ) . in comparison , for h - siw11c16 there are only 
 few aggregates found by dls with sizes small enough for ordinary micelles . the dls data are consistent with tem 
 investigations ( figure 3d ) , which show objects with 25 nm in length and 57 
 nm in width . however , one can clearly see there is an asymmetric distribution 
 of contrast ( figure 3e ) . each aggregate has dumbbell shape with two zones of high electron 
 density opposite to each other and an area of lower imaging contrast 
 between . however , we were only able to fit the saxs curve of h - pw11c16 with a core  shell model ( figure 3f ) . due to the very high electron density 
 of the pom clusters forming the edge of the aggregate , the development 
 of a dumbbell core  shell model  would be of 
 certain interest for the simulation of the saxs curve obtained for 
 h - siw11c16 .. to the best of our knowledge , 
 such a micellar morphology is unique . 
 at higher magnification , the area in the middle seems to comprise 
 a lamellar substructure ( figure 3e ; bottom particle ) . despite the fact the geometry 
 of the pw11c16 , siw11c16 , and bw11c16 surfactants is the same , undoubtedly 
 the difference in headgroup charge leads to marked effects for the 
 self - organization processes . pw11c16 with a 
 headgroup charge of  3  still behaves like an 
 ordinary surfactant . cylindrical 
 llc phases and at lower concentration in water spherical , micellar 
 aggregates ( scheme 1b ) . in the current contribution , 
 we showed the synthesis and characterization 
 of a series of three polyoxometalate surfactants with the same structure 
 and dimensions but different charges : [ pw11c16 ] , [ siw11c16 ] , and [ bw11c16 ] . there 
 is another important factor in aqueous pom - systems , which is cation - mediated 
 attraction . is has been shown among others by liu and weinstock that self - assembly 
 of pom clusters is affected by the counterions . molecular dynamic 
 simulations of keggin clusters in acid aqueous environment performed 
 by chaumont and wipff also show that 
 siw12o40 exhibits a larger 
 tendency of aggregation compared to pw12o40 , despite its higher charge . furthermore , they found 
 that the distance between the aggregated clusters changes only marginally 
 ( 0.1  ) . transferring these findings to our systems , one can 
 conclude that our assumptions on the equality of the headgroup sizes 
 of the herein - analyzed surfactants are correct . despite the fact we 
 can not quantify the influence of cation - mediated attraction , our assumptions 
 are still valid as the systems comprise the same sort of cations in 
 the compared low- and high - concentration regimes . we investigated 
 the formation of lyotropic structures in water 
 at high and at low concentration . we found that there is a substantial 
 influence of charge on the self - organization behavior . 3  , perfectly matched the structures one would 
 expect for classical surfactants with the help of the concept of the 
  packing parameter  . when the headgroup charge is even higher , as for bw11c16 , it was pointed out the emergence of ordered 
 aggregates is aggravated . although we can not give a precise 
 physical picture of the interactions 
 and thermodynamics leading to the unusual phenomena , we want to discuss 
 some ideas and check if they are in - line with existing theories on 
 surfactant self - assembly . considering the 
 inspiring seminal work of grzybowski and co - workers on nanoparticle 
 self - assembly , one condition for achieving 
 unprecedented modes of self - assembly is the existence of competing 
 attractive and repulsive forces . the attractive forces in the current 
 molecular system are of course the interaction of the head with cations 
 and the van der waals / hydrophobic interactions between the alkyl - chains , 
 just like in any other surfactant system . as classical surfactants carry only a low headgroup charge , the 
 electrical field is too weak to result in a substantial repulsive 
 force . the electrical field originates from unshielded charge , caused 
 by the unbalanced distribution of the counter cations around the pom 
 headgroup , as they can not be situated in the hydrophobic domains of 
 the aggregate . as a consequence , one observes known structures dictated 
 by the attractive interactions . as such compact and highly charged 
 surfactants like described in our work were not considered when israelachvili 
 and co - workers published their popular work , is not surprising that 
 our systems exceed the limitations of the packing parameter . as a 
 very rough model , we consider the electric field resulting from a 
 polyoxometalate cluster treated as an isolated point - charge fixed 
 of a surface ( of an dielectric medium of low polarizability ) immersed 
 in an electrolyte with a helmholtz - type layer of cations attached 
 to the headgroup . the contribution of the attractive , hydrophobic 
 interactions is constant in both systems ( pw11c16 and siw11c16 , indicated by black arrows in scheme 1 ) . whereas the repulsive 
 electrostatic force ( green and red arrows ) grows stronger with a higher 
 charge of the surfactant and eventually crosses the threshold repulsive 
 interaction starts influencing the self - assembly behavior . because 
 of a high headgroup charge , it would be favorable for siw11c16 also at high concentration to form curved structures , 
 which militates against a classical lamellar phase . besides , the high 
 charge could also increase the packing parameter of the surfactant , 
 and this is also a factor favoring curved aggregates . due to the described 
 electrostatic repulsion , siw11c16 can not adopt 
 cylindrical aggregates as easily as this would require interdigitation 
 of the alkyl - chains and thus a smaller distance between the negative 
 poles , which is obviously disadvantageous . thus , the bilayer aggregates 
 can be seen as a compromise between a cylindrical structure and a 
 lamellar phase . it can be argued that at lower concentration , water 
 molecules might penetrate the interlayer space comprising the pom 
 heads and their counterions . the bisection of the lamellar structure 
 and reorganization of the aggregates is the result ( see scheme 1a ) . the solvation of the cations 
 leads to a further increase of the packing parameter , and normally 
 a micelle , the structure with the maximum curvature , is formed ( scheme 1b ) . because of the 
 same reasons given above , siw11c16 can also 
 not exist in the state of spherical micelles so easily , and again 
 one can rationalize the emergence of a new pattern ( figure 3d , e ) caused by the necessary 
 compromise . the process can be thought to result from the transition 
 of the bilayer plates on its two flat sides , which could explain the 
 symmetry of the dumbbell objects , the overall extensions of those 
 particles , and the central , lamellar subdomain with weak electron 
 contrast ( scheme 1b , 
 right image ) . this morphology is distinct from dumbbell micelles for 
 purely organic systems described in some theoretical predictions , 
 but there are similarities . for instance , leermakers predicted anisotropic , 
 elongated micelles , if the length of the alkyl - chain is small , which 
 could lead to an enhanced repulsion between the heads in an aggregate . argue the formation of dumbbell 
 micelles can be the effect of a curvature - driven nanophase separation . this model is of course oversimplifying the 
 real situation , but , unfortunately , quantitative calculations would 
 require sophisticated ab initio calculation , which can only be done 
 by specialists .
nonequilibrium states of matter are 
 arousing huge interest because 
 of the outstanding possibilities to generate unprecedented structures 
 with novel properties . 
 self - organizing soft matter is the ideal object 
 of study as it unifies periodic order and high dynamics . 
 compared 
 to settled systems , it becomes vital to realize more complex interaction 
 patterns . 
 a promising and intricate approach is implementing controlled 
 balance between attractive and repulsive forces . 
 we try to answer 
 a fundamental question in surfactant science : how are processes like 
 lyotropic liquid crystals and micellization affected , when headgroup 
 charge becomes so large that repulsive interactions are inevitable ? 
 a particular challenge is that size and shape of the surfactant must 
 not change . 
 we could realize the latter by means of new hybrid surfactants 
 with a heteropolyanion head [ ew11o39]n ( e = pv , siiv , biii ; n = 3 , 4 , 5 ) . among the unusual 
 self - assembled 
 structures , we report a new type of micelle with dumbbell morphology .