Surfactant-directed self-assembly

Brinker and coworkers also prepared photoresponsive nanoporous silica particles using aerosol-assisted assembly, EISA, and surfactant-directed self-assembly (SDSA) techniques (Liu, 2004). The as-prepared photoresponsive nanocomposite particles were prepared so that the azobenzene ligands pointed toward the hydrophobic micellar interiors. After surfactant removal by solvent extraction, nanoporous particles with azobenzene ligands positioned on the pore surfaces were formed (Fig. 13.8). 

Finally, the synthesis of PMOs involving surfactant-directed self-assembly and self-directed assembly allows reaching a multiscale structuration of the material with controlled optoelectronic properties. 

In the second approach to self-assembly of polymer-silica nanocomposites, polymerizable surfactants are employed both to direct self-assembly into ordered mesophases and to serve as organic monomers which can be subsequently polymerized. For instance, Brinker et al. developed nonionic surfactants incorporating diacy-telene groups which could be polymerized upon irradiation by UV light.68 69 Similarly, poly(thiophene)70 and poly(pyrrole)71 have been successfully integrated into silica nanostructures in this manner. Importantly, this in situ polymerization produces isolated molecular wires, rather than clustered bundles of conductive polymer.70... 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

Generally, the mechanism proposed for structure direction and self-assembly in the synthesis of Si-ZSM-5 involves the formation of an ordered, hydrophobic hydration sphere around the TPA cation [11]. The assembly process of MCM-41 is controlled by electrostatic interaction between silicate species and charged surfactant head groups [12]. 

An example of the first approach is the integration of hydrogels into nanostructured silica films by addition of a suitable monomer (e.g., methyl methacrylate, /V-isopropyl acrylamide, etc.) and an initiator for radical polymerization to a solution containing a structure-directing surfactant and a prehydrolyzed silica precursor. During self-assembly, the monomers partition within the hydrophobic core of the surfactant mesophase postsynthesis polymerization (for instance, by UV treatment) followed by solvent washing to remove the surfactant template yields a polymer-silica nanohybrid. 

Figure 18.6 Fabrication of polymer-silica mesostructured materials through a self-assembly process by (a) addition of reactive monomers to the precursor solution, followed by postdeposition polymerization (b) addition of a polymerizable surfactant and (c) direct addition of a soluble polymer to the synthesis solution.

Since these arborols (111) are comprised of two hydrophilic groups connected by a hydrophobic linkage, they fit the simple definition of a bolaamphiphile a term derived from bolaform amphiphile, originally introduced in 1951 by Fuoss and EdlesonJ128 In 1984, when Fuhrhop and Mathieu 129 reported the synthesis and self-assembly of several bolaamphiphiles, these two-directional surfactant-like macromolecules represented a simple entrance to the bolaamphiphile field this subject has recently been highlighted1130 and reviewed.1131 ... 

Considerations of the packing parameter concept of Israelachvili et al. [1] suggest that double-chain surfactants, which form the basis of measurements described in this article, cannot readily form spherical micelles. With double-chain surfactants, a more likely aggregate structure is the formation of bilayer vesicles, which can be also thought of as a dispersed lamellar phase (La) as such the vesicular dispersed form is likely to be preferentially formed at low concentrations ( 1 mmol dm-3) of surfactant. Furthermore, it is necessary to consider the possibility, unlike in the case of micelles, that such vesicles, formed by self-assembly of surfactant monomers, will not be thermodynamically stable. The instability is then likely to be in the direction of growth to a thermodynamically-stable lamellar phase from the vesicles. This process will be driven, at least initially, by fusion of two vesicles. 

We have developed a variety of experimental techniques to control the geometry, dimensionahty, topology, and functionality in surfactant membranes that can be directly useful in nanoscale network and device design [11-13]. Methods based on self-assembly, self-organization, and forced shape... 

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