Novel polymer gels based on phase structure of aqueous dispersion of polymer microgels

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Phase transition of aqueous dispersions of monodisperse poly(N-isopropylacrylamide) microgels was investigated. From the phase diagram drawn on the basis of the diffracted light from the dispersions, it was found that the critical crystallization volume fraction was independent of temperature, which indicates that phase transition in this colloidal system was dominated by repulsive inter-particle interaction. The relaxation dynamics of the concentrated dispersions was investigated by a dynamic light scattering technique. In liquid phase above the melting temperature, usual translational diffusion of the particles was observed. In contrast, the diffusion coefficient in crystalline and glassy states increased with decreasing temperature despite the increasing size of the microgels. Gels synthesized by the subsequent polymerization in the presence of the microgels had a good extension strength compared to the conventional ones without the microgels.