Gelation of Polymer Solution and Percolation Model

本课题拟从聚合物溶液凝胶化与相变或相分离动力学统一理解的角度，研究渗透模型的有效性。我们对聚合物溶液凝胶化的示踪和生长团簇的表征进行了研究，表征了聚合物分子凝胶具有独特的相行为，以及对相变的多分散性效应。我们主要利用光散射技术，分析了相关函数的衰减率分布。为了定量评价反应的程度，还对辐射诱导聚合和凝胶体系进行了研究。对于在极稀条件下发生凝胶化的多糖，在团簇强度和大小上发现了异常，并显示出服从幂律。对于辐射诱导凝胶，胶凝点难以准确确定。相关函数在凝胶点处表现为幂律行为，多糖和辐射诱导凝胶的指数在0.6 ~ 0.7之间，与化学凝胶相差较大。物理凝胶和化学凝胶有质的区别。确定了非遍历性的程度与凝胶化密切相关。观察到相分离（解裂-生长）与凝胶之间的耦合现象。对于表现出溶胶-凝胶转变和体积相变的聚合物，进行了分子表征，得到了这种独特相行为的分子水平上的碱基。特别澄清了不连续体相变的成因。

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.