Polymer gels and surfactants - Their interactions and hybrid materials

Up-to-date research results on the interactions and hybrid materials betwee n polymer hydrogels and surfactants have been overviewed. The volume phase transition behavior of poly(N-isopropylacrylamide) gel (NIPA) is dramatical ly changed on addition of some surfactants, depending upon the chemical str ucture of the agents. In order to elucidate the above, binding isotherms of the surfactants onto the NIPA gel have been measured. Discontinuous and re versible binding was first observed in the NIPA gel/ionic surfactant system s. The phase transition of the gel also took place at the same concentratio n of the agent as that of the discontinuous binding. The binding affinity o f surfactants is, then, switched by the conformational change of the polyme r chains through its phase transition. This affinity switching is a good mi mic of protein functions such as oxygen uptake of hemoglobin and/or catalyt ic process of enzymes. The increments of the phase transition temperature o f the NIPA gel on addition of a surfactant are linearly related to the bind ing amount of the agent at the transition point. This means that the bindin g ability of surfactant governs the phase transition temperature of NIPA ge l. A hybrid material of polymer hydrogels and bilayer membranes has been fi rst synthesized and characterized. A polymerizable surfactant, 2,3-dihydrox ypropyl dodecyl itaconate (DDI),forms an iridescent solution resulting from a periodic structure of bilayer membranes. This iridescent lamellar struct ure of DDI can be photo-polymerized by UV-light together with water-soluble monomers such as acrylamide, NIPA and N,N-methylenebisacrylamide (a cross linker). The bilayer-membranes-immobilized polymer gels thus obtained show some unique properties that are not obtained from either component. Anisotr opic gels obtained by photo-polymerization after shear flow of the monomer mixtures show interesting anisotropic behaviors in swelling, optical and me chanical properties.