Polystyrene reversed micelles

Surfactants and Colloids in Supercritical Fluids Because very few nonvolatile molecules are soluble in CO2, many types of hydrophilic or lipophilic species may be dispersed in the form of polymer latexes (e.g., polystyrene), microemulsions, macroemulsions, and inorganic suspensions of metals and metal oxides (Shah et al., op. cit.). The environmentally benign, nontoxic, and nonflammable fluids water and CO2 are the two most abundant and inexpensive solvents on earth. Fluorocarbon and hydrocarbon-based surfactants have been used to form reverse micelles, water-in-C02... 

As depicted in Fig. 5a, the diblock copolymer polystyrene-bfock-poly (2-vinylpyridine) (PS- -P2VP), consisting of a hydrophobic apolar PS block attached to a hydrophilic polar P2VP domain, is widely used to prepare ordered monolayers of inorganic nano-objects. The solubilisation of PS- -P2VP in toluene leads to the formation of homodisperse reverse micelles made of a hydrophilic P2VP core and a hydrophobic PS outer shell interacting with the solvent molecules. 

In addition, polymer micelles have been demonstrated to be more stable and also have a significantly lower cmc than surfactant micelles. Further discussion of surfactant micelles is beyond the scope of this review, and, instead, the reader is directed to a recent review article by Armes. In fact, the polymer building blocks need not be amphiphilic and such phase-separated nanostructures can be formed from completely hydrophobic or lipophilic diblock copolymers that contain two segments with differing solubility (such as polystyrene- -polyisoprene) and hence can undergo phase separation in selective solvents. One example of such completely hydrophobic phase-separated micelles are those reported by Wooley and coworkers, which can be obtained from toluene and acetone solutions of a [polystyrene-a/f-poly(maleic anhydride)]-fc-polyisoprene Iriblock. Conversely, inverse structures are also accessible and are known as reverse micelles. These can be formed by adding a nonsolvent for the hydrophilic block to afford the opposite of a conventional micelle, for which the hydrophilic core is surrounded by a hydrophobic shell in a hydrophobic surrounding media. There have been a handful of reports on the application of these reverse micelles, for example, as nanoreactors and for the extraction of water-soluble molecules. ... 

Iron oxide nanocomposites have been prepared by hydrolysis of iron salts in sulfonated polystyrene resins, mesoporous sulfonated styrene-divinylbenzene copolymer, acrylonitrile-methyl methaciylate-divinylbenzene copolymer, cross-linked high amylose starch, polyimides, polyvinylpyridine, polypyrrole,eellulosies. Nanocomposites of metals (Cr, Mo, W, Fe, Co, Ni) with a variable particle size (2-10 mn), have been prepared from solutions of metal preeursors in a molten polymer (polyethylene, polypropylene, polytetra-fluoroethylene, polyamide, polyaiylate, polycarbonate, polystyrene, polyethers, polyphenyleneoxide, siloxane). There are also many examples of in-situ precipitation of iron oxides in aqueous solution of polymers, such as dextran, PVA, polyethylene glycol, etc. In this case, size dispersion and aggregation are frequent, but they can be minimized by using reverse micelles. ... 

Block copolymers in a selective solvent, ie., a good solvent for one block but a precipitant for the other, behave like typical amphiphiles. The copolymer molecules aggregate reversibly to form micelles in a manner analogous to the aggregation of classical surfactants. Our block copolymers are very amphiphilic in the sense described above and form well-defined micelles in a wide range of selective solvents. In solvents for polystyrene, the polystyrene block is located in the micelle corona, while the modified block is hidden in the micelle core. 

Stepanek M, Matejicek P, HumpoKckova J, Prochazka K (2005) Reversible aggregation of polystyrene-Woci-poly(2-vinylpyridine)-W(3cl -poly(ethylene oxide) block copolymer micelles in acidic aqueous solutions. Langmuir 21 10783-10790... 

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