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

本研究计划从介观尺度研究聚合物凝胶的物理化学特性和体积相变，并考虑凝胶内部的非均质性。主要研究了PNIPAM和PNnPAM凝胶小球的热响应。为了表征这种与尺寸效应有关的热响应，我们试图通过各种合成方法来获得微米级的单分散凝胶小球，并获得了与体积相变相关的各种重要发现。在微米级凝胶与丙烯酸共聚的情况下，处于溶胀状态的对称凝胶微珠在高温下收缩成不对称的形状。这是因为足够长到这样大小的凝胶含有不均匀的网络结构，这导致了不对称的收缩。这意味着研究中尺度上详细的网络结构的重要性。此外，通过凝胶微珠悬浮液的超声速度可以评价水合水分子数在体积相变过程中的变化，与理论预测吻合较好。为了在真实空间中观察凝胶网络，将共聚焦激光扫描显微镜应用于纤维蛋白生物凝胶，成功地弄清了凝胶网络的骨架，得到了凝胶网络的分维。所得尺寸与动态光散射测量结果吻合较好。从而阐明了详细表征凝胶介观结构的重要性。

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.