Kinetics of Phase Transitions of Polymer Gels

这项研究旨在建立聚合物凝胶相变动力学的物理和化学原理；相变是一种普遍存在于凝胶中的现象，即随着温度、溶剂组成、pH、离子强度、电场或光线的变化，凝胶的体积可逆地膨胀或收缩多达1000倍。这项研究将考察不同尺寸和化学成分的凝胶的形状、局部网络密度和局部应变的时间进程，涉及相变的动力学过程。凝胶的膨胀或收缩过程相对于体积的微小变化的动力学已经被建立；它唯一的特征是聚合物网络的集体扩散系数。类似的理论是否适用于凝胶体积变化3个数量级的相变动力学尚不清楚。为了检验这一假设并建立相变动力学原理，这些粘弹量将在凝胶的整个相图中独立确定。摩擦系数和剪切模数将由微观方法确定。将使用动态光散射和荧光光漂白恢复光谱。在经历相变的凝胶中出现的图案的形成和演变的机制将被阐明，从而形成支配凝胶动力学过程的运动方程。最后，希望阐明凝胶中结构不均匀的来源，这些结构不均匀对凝胶的机械、光学和粘弹性性质有很大影响。

This research aims to establish the physical and chemical principles which underlie in the kinetics of the phase transition of polymer gels; phase transitions are a phenomenon universally found in gels where they reversibly swell or shrink in volume by as large as 1000 times in response to changes in temperature, solvent compositions, pH, ionic strength, electric field, or light. The research will examine the time course of the shape, local network density and local strain of gels of various sizes and chemical composition in regards to the kinetic processes of a phase transition. Kinetics of a swelling or shrinking process of a gel with respect to a small change in volume have already been established; it was uniquely characterized by the collective diffusion coefficient of polymer network. Whether or not a similar theory applies to the kinetics of phase transition where the gel volume changes by 3 orders of magnitude is unknown. To examine such a hypothesis and establish the principles of kinetics of phase transition, these viscoelastic quantities will be independently determined within the entire phase diagram of gels. Friction coefficient and shear modulus will be determined by microscopic methods. Dynamic light scattering and fluorescence photobleaching recovery spectroscopy will be used. The mechanism of formation and evolution of patterns that appear in gels undergoing a phase transition will be elucidated so as to formulate the equation of motion that govern the kinetic processes of gels. Finally, it is hoped to clarify the origin of structural inhomogeneities within gels which influence substantially their mechanical, optical, and viscoelastic properties.