Gelation of Polymer Solution and Percolation Model

本课题从聚合物溶液的凝胶化可以与相转变或相分离的动力学统一理解的观点出发，研究逾渗模型的有效性。我们进行了高分子溶液凝胶化的示踪和生长团簇的表征、凝胶具有独特相行为的高分子分子的表征以及多分散性对相变的影响的研究。我们主要采用光散射的方法，分析了相关函数的衰减率分布。为了定量评价反应程度，还对辐射引发聚合和凝胶体系进行了研究。对于在非常稀的条件下发生凝胶化的多糖，检测到异常的簇强度和尺寸，并且它被示出服从幂律。对于辐射诱导凝胶，其凝胶点的准确测定比较困难。相关函数在凝胶点处呈幂律行为，多糖和辐射诱导凝胶的指数约为0.6-0.7，与化学凝胶有较大差异。物理凝胶与化学凝胶有质的区别。据确定，非遍历性的程度是密切相关的凝胶化。观察到相分离（成核-生长）和凝胶化之间的耦合现象。对表现出溶胶-凝胶相变和体积相变的聚合物进行了分子表征，为这种独特的相行为提供了分子水平上的依据。特别阐明了不连续体积相变的起源。

This project was planned to study the validity of percolation model from the viewpoint that the gelation of polymer solution can be understood unifiedly together with the dynamics of phase transition or phase separation. We carried out the study of tracing to gelation of polymer solution and chracterization of growing clusters, characterization of polymer molecules the gel of which exhibits unique phase behavior, and polydispersity effect to phase transition. We used light scattering mainly and analyzed the decay rate distribution of the correlation functions. In order to evluate the degree of reaction quantitatively, radiation-induced polymerization and gelation system was also studied. For polysaccharide where gelation occurs at very dilute condition, anomaly was detected in cluster intensity and size, and it was shown to obey the power-law. For radiation-induced gel, it was difficult to determine the gelation point accurately. Correlation function shows power-law behavior at the gelation point, and the exponents for polysaccharide and radiation-induced gel were about 0.6-0.7 showing a big difference from the chemical gel. There exists a qualitative difference between physical and chemical gel. It was ascertained that the extent of nonergodicity is correlated strongly with the gelation. Interesting phenomena for the coupling between the phase separation (uncleation-growth) and the gelation was observed. For the polymers which exhibit sol-gel transition and volume phase transition, molecular characterization was carried out and the bases at the molecular level for such unique phase behavior were obtained. Especially, the origin of discontinuous volume phase transition was clarified.