Simulation on the Kinetic Process in Polymer-Dispersed Liquid Crystals

• Main Authors: Chen, Wei-Jou, 陳威州
• Other Authors: Shu-Hsia Chen
• Format: Others
• Language: en_US
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/33184661656818598433

博士 === 國立交通大學 === 光電(科學)研究所 === 84 === 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