Swelling surfactant-polymer systems

The phenomenology of physical organogels and jellies is extremely rich, and their comportments are similar in some aspects to those of both surfactants in solution (e.g., lyotropism and crystallization) and polymer solutions (6 (e.g.. swelling/shrinking behaviors and microscopic mass motion). Gels can be considered as being at the interface between complex fluids (i.e.. micellar systems) and phase-separated states of matter. The main properties and concepts appropriate to describe the gels and the basic principles of techniques for their study will be reviewed here. 

Core-Shell Latexes. First a seed latex of polymer 1 is synthesized. Then, a second monomer is added to the system, usually with no added surfactant. Often, a starved polymerization route is employed, i.e., the rate of polymerization equals or exceeds the rate of monomer addition. This reduces the swelling of the seed latex by monomer 2, producing a two-layer latex having a spherical core, and an overlaying shell. Obviously, multiple shells can be added. 

Instabilities that manifest themselves in surfactant and polymeric systems have been considered in an attempted to elucidate the myelin instability. In polymer-like micelles (or wormlike micelles) instabilities have been observed in the directional growth of hexagonal phases in a temperature gradient (30), These instabilities are an example of the Mullins and Sekerloi type (31), In the case of polymer gels, instabilities appear during growth, which resemble a raspberry like texture at the surface. This instability is due to the elastic properties of the gel which is a network of chemically bonded polymers. As the gel swells at the surface it remains anchored to the rest of the unswollen gel and the surface buckles (50). 

Figure 20.31. While a hydrophilic polymer enriches in the lower aqueous phase of a three-phase system and destabilizes the microemulsion phase, the corresponding hydrophobically modified polymer, which associates to the surfactant films, is incorporated in the microemulsions and stabilizes them. This is illustrated here by a schematic of the relative phase volumes as a function of the polymer concentration. The initial swelling of the middle phase is reversed at higher polymer concentrations when the middle phase has been saturated with polymer (Qat)- (Redrawn from A. Kabalnov, B. Lindman, U. Olsson, L. Piculell, K. Thuresson and H. Wennerstrbm, Colloid Polym. ScL, 274 (1996) 297)...

This chapter aims also to cover a related topic, that of less-perfect-than-model, albeit functional, conetworks. These materials exhibit some control in their stmcture but are not defect-free. Furthermore, they comprise polymer segments or blocks of two different monomers. This arrangement may lead to microphase separation either in the bulk or in selective solvents. Most reports concern studies of amphiphilic conetworks (APCNs) in water, which are systems combining the properties of surfactants and hydrogels. Hius, these materials swell in water, but less so than purely hydrophilic gels. Moreover, they self-assemble to form miceUe-like hydrophobic cores however, this takes place under the constraints of the conetwork aoss-links. 

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