柔性高分子/液晶共混体系的相分离初期动力学

Early stage phase separation kinetics in flexible polymer/liquid crystal mixture

由Flory－Huggins的柔性高分子溶液的格子模型和Lebwohl－Lasher液晶模型结合起来导出的高分子／液晶复合体系的混合自由能泛函，并引入TDGL方程以用描述体系的相分离动力学．线性化理论的计算结果表明．高分子／液晶复合体系的相分离初期行为与描述普通两元熔体的相分离初期的Cahn－Hilliard理论结果十分相似，即在Spinodal区域内，浓度涨落（即散射光强）随时间变化呈指数式增长，而散射函数的峰值位置（qm），则不随时间而改变．另外，高分子／液晶体系有两个Spinodal相区域，即各向异性Spinodal相区域和各向同性Spinodal相区域．而且，处在各向异性态的液晶能强烈地排斥柔性高分子，因而在各向异性相区域的相分离初期速度要比各向同性区域快得多，散射光强也要强得多．

In this paper, Lebwohl-Lasher model of nematogens and Flory-Huggins latticemodel of polymers have been combined to derive the free energy function of polymer/liquidcrystal mixture. By incorporating this free energy into TDGL equation,the kinetics of phaseseparaTion in polymer/liquid crystal mixture is described. The result of linear theory showsthat the phase separation behavior of polymer/liquid crystal mixture at early stage is similarto that o conventional binary melts,which have been treated by Cahn-Hilliard theory,that is,in spinodal regime, the concentration fluctuation (i. e. light scattering intensity) grows up exponentially with time but the position of the maximum of scattering function,qm,doeos notchange with time. Besides,the polymer/liquid crystal mixture has two spinodal regime,i. e.,nematic spinodal regime and isotropic spinodal regime. Moreover,because the liquid crystal innematic state repels flexible polymer strongly,so that the speed of early stage phase separation in nematic spinodal regime will be accelerated and the scattering intensity will also bemuch stronger than that in isotropic spinodal regime.