Statistical-Mechanical Study of Phase Formation in Thermoreversible Gels

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We developed a new theory ("Solution Theory of Associating Polymers") to derive phase diagrams of thermoreversible gels. This theory is a combination of the lattice-theoretical polymer solution theory developed by Flory and Huggins, and the classical theory of gelation (tree statistics) established by Flory and Stockmayr. It describes chemical equilibrium among polymers.(1) By this new theory, we derived phase diagrams of complex fluids including homopolymer gels, hydrated gels, interpenetrating gels, gels accompanied by polymer comformation change, etc. We showed new multicritical phenomena appear as a result of the competion among sol/gel transition, microphase separation and macrophase separation.(2) On the basis of these results, we are now developing on a work station a computer system for the prediction of complex phase diagrams from molecular design of constituent polymers. This system will serve as a simulation system to help material developments.(3) We also developed a theory of visco-elasticity of thermoreversible gels. This is called "Transient Network Theory", and provides a good starting point to study, for examle, movement of biiological cells by repeated sol/gel transition and viscosity-controlling polymers called "thickner". Some reserch groups in Eulope and U.S.A.are producing experimental data to compare with our theory.