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

聚合物凝胶中的表面态和反常一级相变

基本信息

批准号：
02640273
负责人：
HIROTSU Shunsuke
金额：
$ 1.28万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02640273/
关键词：
Polymer Gel Surface State Light Scattering Surface Potential Volume Phase Transition 表面張力

项目摘要

(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.

(1)凝胶整体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，例如溶胀度和相变温度，很大程度上取决于样品的形状。目前的研究致力于阐明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异常大的表面张力，另一种是基于在凝胶化时冻结的一些结构缺陷。对不同凝胶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，尚未进行表面张力的直接测量，因此我们不能得出第一种机制是合理的结论。(2)电离凝胶表面电位的测量。首先使用Ag-测量电离凝胶的表面电位。 AgCl微电极。已证实，在中性凝胶中表面电位消失，而在离子化凝胶中检测到几十到几百mV的表面电位。该值取决于凝胶网络中所含离子的量。该结果支持电离凝胶中电化学来源的表面张力的存在。需要进一步详细的测量才能获得更定量的结果。(3)凝胶网络动态不均匀性的测量。最初，我尝试通过激光散射来测量凝胶的表面激发，以获得表面状态的详细信息。然而，事实证明这是一项相当困难的测量，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，我测量了凝胶响应温度跃变从一种平衡状态转变为另一种平衡状态时表现出的大规模波动。根据这一结果，出现了接近体积转变的玻璃状凝胶模型。