含液晶滴之聚合物形成過程的動態模擬

Abstract

本論文研究含液晶聚合物形成過程。在一般條件下，含液晶聚合物是由起 初均勻混合的液晶分子與聚合物單體分子，在一連串的高分子聚合化學反 應下誘發液晶分子與高分子分離而形成的。其形成過程是一高分子聚合誘 發相分離的過程。而在液晶分子與聚合物單體分子具有高粘滯係數或高分 子聚合化學反應極快速的條件下，含液晶聚合物的形成過程可視為一在具 有固定不動的非等向性液晶分子中的高分子聚合過程。首先，我們考慮在 含液晶聚合物的形成過程中，液晶分子與聚合物單體分子具有高粘滯係數 或高分子聚合化學反應極快速的條件下，提出一高分子在固定不動的非等 向性液晶分子中的聚合糢型。從這模型的研究，我們發現在非等向性液晶 的有序參數不為零的條件下，聚合成的網狀高分子同樣具有非等向性的結 構，此結果與最近在實驗上用電子顯微鏡所觀測的結果相符。此外，我們 得到此系統可凝膠化與不可凝膠化的相圖。利用有限尺寸的尺度分析，來 分析高分子的平均分子量，凝膠化程度及迴旋半徑，我們發現此一高分子 聚合模型在凝膠化轉變的臨界指數與滲透模型是一樣的。進一步，在一般 的條件下，即液晶分子與聚合物單體分子可適度流動，我們提出另外一個 模型來研究高分子聚合誘發相分離的過程。此一模型的研究，可得到實驗 上所觀測到的結構參數凍結現象。從動態結構參數的尺度分析中，我們得 到一動態尺度律，此一尺度律與熱致相分離研究所得的尺度律相同，並與 最近實驗所得相符。此外，此模型可由一組尺度律來分析高分子誘發相分 離的凍結結構及達到此凍結結構的時間與起始劑濃度的關係。我們提出一 理論分析而得此尺度律的指數並與模擬結果相符。從液晶分子團的尺寸分 析，我們還發現了在實驗上觀察到的二次相分離現象。 The subject of this thesis is to investigate the formation process of a polymer-dispersed liquid crystals (PDLC). In general, PDLC materials are formed from the phase separation derived by chemical polymerization of an initially homogeneous mixture of liquid crystals and monomers. The formation process is referred to as a process of polymerization-induced phase separation. For polymerization with fast reaction rate or the molecules of liquid crystal and monomer with high viscosity, the formation process of PDLC is regarded as a process of polymerization in a quenched anisotropic nematic medium. First, we propose a model to study the polymerization in a quenched anisotropic nematic solvent for the system in which the time scale for polymerization is short compared to that for the mobility of the anisotropic nematic solvent or monomers. The structure of a polymer network was found to be extended in the direction of the director of the anisotropic nematic solvent, as the order parameter of the anisotropic nematic solvent is nonzero. The experimental observation of scanning electron micrograph is consistent with our simulation results. In addition, we construct a phase diagram of gel-nongel for the kinetic gelation system. Finite-size scaling analyses for the average molecular weight, gel fraction, and radii of gyration show that the critical exponents of the sol-gel transition is the same as that of percolation. Furthermore, we propose a dynamical model to study the polymerization-induced phase separation for taking into account the mobile behavior of a liquid crystal and a monomer. A pinning phenomenon of the structure factor was found and consistent with experimental observation. The time evolution of the structure factor was found to preserve the scaling law obtained from the thermally quenched phase separation as well as the recent experiment. In addition, The model leads to the revelation of scaling relations of pinned structure factor and crossover time with a