Study of Volume Phase Transition of Polymer Gel from the Mesoscopic Region

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This research project was planned to study the physicochemical characteristics and volume phase transition of polymer gel from the mesoscale region with regard to the inhomogeneity inside the gel. Thermal response of gel beads of PNiPAM and PNnPAM were studied mainly. In order to characterize such a thermal response relating to the size effect, we tried to obtain the monodisperse gel beads with micron size by various synthesizing methods, and various important findings relating to the volume phase transition were obtained. In case of micron size copolymerized gel with acrylic acid, symmetric gel beads at the swelling state shrink to asymmetric shape at high temperature. This results from that the gel, which grows sufficiently upto such a size, contains inhomogeneous network structure and this causes asymmetric shrinkage. This means the importance of studying the detailed network structure in the mesoscale. Moreover, by the ultrasonic velocity of gel beads suspension, the variation of the number of hydrated water molecules in the course of volume phase transition was able to be evaluated, and is in fairly good agreement with the theoretical prediction. In order to observe the gel network in real space, confocal laser scanning microscopy was applied to the biological gel of fibrin, and we succeeded to clarify the backbone of gel network and obtained the fractal dimension. The obtained dimensions were in good agreement with the results determined by the dynamic light scattering measurements. Thus, the importance of detailed characterization of mesoscopic structure of gels was clarified.