Studies on Gelation and Slow Dynamics on Connectivity-Correlated Polymeric Systems

聚合物凝胶可以看作是一种连接性相关的聚合物体系。凝胶中存在多种类型的不均匀性，这些不均匀性对凝胶的表征和凝胶化阈值起着重要作用。然而，非均匀性之间的差异及其物理含义尚未在文献中广泛讨论。为了阐明这些问题，我们进行了一系列的研究，溶胶-凝胶转变的各种类型的凝胶体系。动态光散射和小角中子散射技术已被用来阐明上述的不均匀性。特别地，动态光散射已被采用以获得重要信息，诸如聚合物链的动态相关性和连接性相关性。用N，N '-亚甲基-双丙烯酰胺（BIS）交联的聚（N-异丙基丙烯酰胺）（NIPA）凝胶经常被称为化学不可逆胶凝体系，其缩写如上所述。这里应该注意的是，使用NIPA凝胶不仅是因为它们的温度敏感性，而且还因为它们与其姊妹凝胶（即，聚丙烯酰胺凝胶结果表明，聚合物凝胶的结构和性质不仅与观察条件密切相关，而且与制备条件密切相关。以明胶和聚乙烯醇离子络合物体系为例，介绍了物理凝胶化体系的热可逆溶胶-凝胶转变和折返溶胶-凝胶转变。动态光散射也表征了β-乳球蛋白的不可逆凝胶化过程。

Polymer gels can be regarded as a connectivity-correlated polymeric system. In a gel, there exist several types of inhomogeneities, which play significant roles in the characterization of gels and gelation thresholds. However, differences among inhomogeneities and their physical implication have not been extensively discussed in the literature so far. In order to elucidate these problems, we carried out a series of investigations on the sol-gel transition of various types of gelling systems. Both dynamic light scattering and small-angle neutron scattering techniques have been employed in order to elucidate the inhomogeneities described above. Particularly, dynamic light scattering has been employed so as to obtain important information, such as dynamic correlation and connectivity correlation of polymer chains. Poly(N-isopropylacrylamide) (NIPA) gels cross-linked with N,N'-methylene-bisacryamide (BIS) was frequently referred to as a chemical-irreversible gelling system with the abbreviations given above. It should be noted here that NIPA gels were employed not only due to their temperature sensitivity but also to their chemical stability against strong bases and acids compared to its sister gel, i.e., polyacrylamide gels. It will be shown that the structure and properties of polymer gels are strongly dependent not only on the observation condition but on the preparation condition. Gelatin and poly(vinyl alcohol)-ion complex systems was introduced as examples of physically gelling systems, undergoing thermoreversible sol-gel transition as well as reentrant sol-gel transition. An irreversible gelation process of β-lactoglobulin was also characterized by dynamic light scattering.