Polymer Gels and Surfactants
--Their Interactions and Hybrid Materials--
The DEEPSTAR Group, Japan Marine Science and Technology Center; 2-15 Natsushima-cho,
Yokosuka-shi 237-0061 Japan
Up-to-date research results on the interactions and hybrid materials between polymer hydrogels and surfactants have been overviewed. The volume phase transition behavior of poly(N-isopropylacrylamide) gel (NIPA) is dramatically changed on addition of some surfactants, depending upon the chemical structure of the agents. In order to elucidate the above, binding isotherms of the surfactants onto the NIPA gel have been measured. Discontinuous and reversible binding was first observed in the NIPA gel/ionic surfactant systems. The phase transition of the gel also took place at the same concentration of the agent as that of the discontinuous binding. The binding affinity of surfactants is, then, switched by the conformational change of the polymer chains through its phase transition. This affinity switching is a good mimic of protein functions such as oxygen uptake of hemoglobin and/or catalytic process of enzymes. The increments of the phase transition temperature of the NIPA gel on addition of a surfactant are linearly related to the binding amount of the agent at the transition point. This means that the binding ability of surfactant governs the phase transition temperature of NIPA gel. A hybrid material of polymer hydrogels and bilayer membranes has been first synthesized and characterized. A polymerizable surfactant, 2,3-dihydroxypropyl dodecyl itaconate (DDI), forms an iridescent solution resulting from a periodic structure of bilayer membranes. This iridescent lamellar structure 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. Anisotropic gels obtained by photo-polymerization after shear flow of the monomer mixtures show interesting anisotropic behaviors in swelling, optical and mechanical properties.
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