Micelles cylinder

One characteristic property of surfactants is that they spontaneously aggregate in water and form well-defined structures such as spherical micelles, cylinders, bilayers, etc. (review Ref. [524]). These structures are sometimes called association colloids. The simplest and best understood of these is the micelle. To illustrate this we take one example, sodium dode-cylsulfate (SDS), and see what happens when more and more SDS is added to water. At low concentration the anionic dodecylsulfate molecules are dissolved as individual ions. Due to their hydrocarbon chains they tend to adsorb at the air-water interface, with their hydrocarbon chains oriented towards the vapor phase. The surface tension decreases strongly with increasing concentration (Fig. 3.7). At a certain concentration, the critical micelle concentration or... 

In water, surfactants form spontaneously defined aggregates such as spherical micelles, cylinders, or bilayers, once the concentration has exceeded the CMC. Which aggregate is formed is largely determined by the surfactant parameter. 

Keywords Block copolymers ABC triblock copolymers Janus micelles Cylinder brushes Core-shell nanoparticles Graft copolymers Micelles Vesicles Copolyampholytes Polyelectrolyte block copolymers Aggregation... 

The special restriction caused by tying low molecular mass liquid crystalline substances to a polymer chain was also illustrated with amphiphilic liquid crystals. A hexagonally close-packed structure of rod-like micelle cylinders of sodium 10-undecenoate with about 50% water lost during polyma-ization at 60 °C its structure and became isotropic. On cooling, a lamellar liquid crystalline structure, more suitable to accommodate the macromolecular backbone was found. Bas l on the discussions of Sect. 5.3.4 it is likely that with longer side-chain amphiphiles condis crystals could be grown in analogy to the soaps described in Sect. 5.2.3... 

In both theories, the concentration of surfactant influences the morphology. In fact, a particular morphology (spherical micelles, cylinders, or lamellas) occurs at a certain concentration range. Ruokolainen et al. estimated that the lamellar morphology is highly preferable for polymer/surfactant systems in the wide concentration range [38]. 

Parallel water-channel (inverted micelle cylinder) model Schmidt-Rohr and Chen quantitatively simulated previously published SAXS data of hydrated Nafion and found that none of the models discussed earlier agree with the SAXS data. They proposed a model featuring long parallel water channels in cylindrical inverted micelles (Figure 2.10)." At 20 vol% water, the water channels have diameters of between 1.8 and 3.5 nm, with an average of 2.4 nm. Nafion crystallites are elongated and parallel to the water channels, with cross sections of about (5 nm). The model with wide parallel water channel can easily explain important features of Nafion, including... 

FIGURE 2.10 Parallel water-channel (inverted micelle cylinder) model for Nafion membrane. (From Schmidt-Rohr, K. and Chen, Q., Nat. Mater., 7(1), 75, 2008.)... 

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

Larger aggregates seldom have spherical geometry, but tend to form cylindrical micelles. In this case, the diameter of the cylinders can usually be adjusted such that the head groups can cover their optimal head group area Uq, and the interaction free energy per surfactant reduces to the constant The size distribution for cylindrical micelles is then exponential in the limit of large N,... 

At small N, correction terms come into play, which account for the ends of the cylinders. In particular, the aggregation number of cylindrical micelles in this simple picture must always be larger than M, the most probable aggregation number of a spherical micelle. Putting everything together, the expected size distribution has a peak at M which corresponds to spherical micelles, and an exponential tail at large N which is due to the contribution of cylindrical micelles. 

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

Figure 3 Example of SANS curves at two times of the reaction. The lines are calculations of the form factor. (A) prior to TEOS addition, the micelles are well described by core-shell spheres, with an external radius of 7.1 ran. ( ) 15 minutes after the beginning of the reaction, the micelles can be viewed as cylinders of length 50 nm and radius 6.9 nm.

The reason why the hybrid micelles evolve from sphere to cylinder is not yet completely understood, but it results from the fact that when silica species are adsorbed onto the surface of the micelles, the average curvature of the micelles is decreasing [9], Polymerisation of silica species by condensation leads to precipitation of the ordered hexagonal mesoporous material. 

Fig. 9 Schematic representation of three approaches to generate nanoporous and meso-porous materials with block copolymers, a Block copolymer micelle templating for mesoporous inorganic materials. Block copolymer micelles form a hexagonal array. Silicate species then occupy the spaces between the cylinders. The final removal of micelle template leaves hollow cylinders, b Block copolymer matrix for nanoporous materials. Block copolymers form hexagonal cylinder phase in bulk or thin film state. Subsequent crosslinking fixes the matrix hollow channels are generated by removing the minor phase, c Rod-coil block copolymer for microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes. (Adapted from [33])...

Figure 4.4 Sudan yellow is a water-insoluble dye, seen at the bottom of the cylinder on the left but fully dissolved in the micelle solution on the right.

Figure 5.10 Self-organization of di-block copolymers. Block copolymers can form spherical and cylindrical micelles, vesicles, spheres with face-centered cubic (fee) and body-centered cubic (bcc) packing, hexagonally packed cylinders (hex) minimal surfaces (gyroid, F surface, and P surface), simple lamellae and modulated and perforated lamellae. (Adapted from Bucknall and Anderson, 2003.)...

From these data it is concluded that the size, shape, and polydispersity of nanoparticles depend critically on the colloidal structure in which the synthesis is performed. This is well demonstrated when, by changing the water content, similar colloidal structures (reverse micelles or interconnected cylinders) are obtained ... 

Fig. 77. Schematic drawing of the liquid-crystal templating mechanism. Hexagonal arrays of cylindrical micelles form (possibly mediated by the presence of silicate ions), with the polar groups of the surfactants (light grey) to the outside. Silicate species (dark grey) then occupy the spaces between the cylinders. The final calcination step burns off the original organic material, leaving hollow cylinders of inorganic material [473]...

---