向列相液晶沿面到垂面排列转变的分子场理论

以摩擦基板间的液晶薄层为研究对象,用分子场理论研究了向列相液晶分子排列转变行为.分子质心固定在简单立方晶格的格点上.液晶由极性分子构成,与基板相接触的一层分子同时受到色散和极性两类表面作用.通过自洽的数值计算,获得3种相图,清楚地展示了摩擦基板间向列相出现的从高温沿面到低温垂面排列的转变;获得实现这类转变所需要的两类表面作用的参数范围.结果表明:基板的摩擦会改变基板表面色散作用,但不会影响基板表面极性作用;表面极性相互作用能引起基板间向列相液晶发生沿面到垂面排列转变.

Molecular Field Theory of the Homogeneous-to-homeotropic Alignment Transition for a Nematic Phase

The molecular field theory is used to invesigate the behaviour of the nematic alignment transition within nematic liquid crystal (NLC) films confined by two rubbed substrates. The molecular centres of mass are located at the sites of a simple cubic lattice. The NLC consists of polar molecules and the molecules of the first layer of the NLC adjacent to the soild bounding surface are affected by both surface dispersion and polar forces. From self-consistent numerical calculations, three types of phase diagram are obtained, which exhibit a transition from a high temperature homogeneous alignment to a low temperature homeotropic alignment. The parameter ranges of two surface interaction which leads to the homogeneous-to-homeotropic alignment transition is obtained. The results show that the surface dispersion action, not the surface polar one, can be changed by the grating of the substrate and the surface polar interaction can give rise to the homogeneous-to-homeotropic alignment transition.