Surface States and Anomalous First-order Phase Transition in Polymer Gels

(1)凝胶体相物理性质的形状依赖性：1990年，我发现聚合物凝胶的平衡性质，如溶胀度和相变温度强烈依赖于样品的形状。目前的研究一直致力于澄清导致凝胶这种非常不寻常的特性的基本机制。提出了两种可能的机制，一种是基于电离凝胶固有的极大的表面张力，另一种是基于在凝胶化时被冻结的一些结构缺陷。对从不同凝胶化条件制备的许多样品进行重复测量，后一种可能性被拒绝。然而，表面张力的直接测量尚未完成，因此我们不能得出结论，第一个机制是一个合理的。(2)离子化凝胶表面电位的测定首次用Ag-AgCl微电极测定了离子化凝胶的表面电位。它被证实，在中性凝胶的表面电位消失，而几十到几百mV的表面电位在电离凝胶检测。该值取决于凝胶网络中所含离子的量。这一结果支持在离子化凝胶中存在电化学来源的表面张力。需要更详细的测量以获得更定量的结果。(3)凝胶网络动力学不均匀性的测量。最初，我试图通过激光散射测量凝胶的表面激发，以获得表面状态的详细信息。然而，这被证明是一个相当困难的测量，因为非常精确的光学对准对于获得有意义的结果至关重要。相反，我测量了凝胶在温度跃变时从一种平衡状态变化到另一种平衡状态时所表现出的大尺度波动。从这个结果，出现了一个玻璃状模型的凝胶体附近的体积转变。

(1) Shape dependence of the bulk physical properties of gels.In 1990, I found that the equilibrium properties such as degree of swelling and phase transition temperature of polymer gels depend strongly on the shape of sample. The present research has been devoted to clarify the basic mechanism leading to this quite unusual characteristics of gels. Two plausible mechanisms are proposed ; one is based on an anomalously large surface tension inherent to ionized gels and the other is based on some structural defects which were frozen at the time of gelation. Repeated measurements on many samples prepared from different gelation conditions, the latter possibility was rejected. However, the direct measurement of the surface tension is not made yet, and thus we cannot conclude that the first mechanism is a plausible one.(2) Measurement of surface potential of ionized gels.Surface potential of ionized gels was first measured using Ag-AgCl microelectrode. It is confirmed that the surface potential Vanishes in neutral gels, whereas several tens to a few hundreds mV of the surface potential was detected in ionized gels. The value depends of the amount of ion contained in gel network. This result supports the presence of surface tension of electrochemical origin in ionized gels. Further detailed measurements are needed for more quantitative results.(3) Measurement of dynamical inhomogeneity of gel network.Initially, I tried to measure the surface excitation of gels by laser light scattering to get detailed information on the surface state. However, it turned out to be a fairly hard measurement because very precise optical alignment is essential to obtain meaningful result. Instead, I have measured a large scale fluctuations exhibited by gels when it changes from one equilibrium state to the other in response to temperature jump. From this results, a glass-like model of gels near the volume transition has emerged.