Dynamiccal Theory of Gelation Process

凝胶化是一种物质从流体状态(在无限小的应力下流动的状态)转变为固体状态(不能流动的状态)的现象。这种现象被认为是无限网络的形成，并经常在渗流理论的框架内讨论，其中研究了当单体或键随机放置在晶格上时，无限网络是何时以及如何形成的。然而，在这种问题的设置中，没有考虑实际的分子动力学。为了研究与凝胶相关的结构演变，我们对链两端有两个反应位置(粘合剂)的遥控聚合物的凝胶过程进行了计算机模拟。我们假设：(I)当贴纸相互接触时，它们形成一簇并一起移动，然后一起移动，并且(Ii)在该簇中存在最大数量的贴纸。研究了凝胶点前后体系的结构演化.发现：(I)随着凝胶点的进行，产生了像调幅分解那样的大的浓度不均匀性；(Ii)这种结构演化在形成无限网络的很长一段时间内发生得非常缓慢；(Iii)结构演化被网络的弹性效应所阻止。

Gelation is a phenomena that a material transforms from a fluid state (the state that flows under infinitesimal strees) to a solid state (the state that cannot flow). The phenomena has been identified as the formation of an infinite network, and has often been discussed in the framework of the percolation theory, where it has been studied when and how an infinite network is formed when monomers or bonds are placed randomly on a lattice \ cite {Family}. However, in such set up of the problem the actual molecular dynamics is not taken into account.Tostudy the structural evolution associated with gelation, we performed a computer simulation for the gelation process of telechelic polymers which have two reaction sites (stickers) at both ends of the chain. We assume that (i) when stickers contact with each other, they form a cluster and move together then after, and that (ii) there is a maximum number of stickers in the cluster. The structural evolution of the system before and after the gelation point is studied.It is found that (i) as the gelation proceeds, a large concentration inhomogeneity is created as in the case of spinodal decomposition, (ii) this structural evolution take place very slowly over the period long after an infinite network is formed, and (iii) the structural evolution is stopped by the elastic effect of the network.