空间各向异性两体势与液晶定向排列

Steric Anisotropic Pair Potential and Alignment of Liquid Crystals

基于分子场理论,研究一种新的空间各向异性两体作用势。对于该两体势,分子质心固定在简单立方晶格的格点上,而势参数依赖于液晶的弹性常数。通过函数迭代方法解分子取向分布函数满足的自洽方程。在大块液晶内部,存在3组单轴解,它们的指向矢分别沿x,y和z轴方向并且具有相同自由能。通过表面作用势描写摩擦后基板对液晶分子的作用,对20个分子层构成的5CB液晶薄层进行了数值计算。仍存在三种指向矢不同的状态,指向矢沿着摩擦方向的状态具有最低自由能。另外,讨论了表面作用在界面分子层中诱导的双轴序。

A new steric anisotropic pair potential is studied based upon molecular field theory. For the pair potential, the molecular centers of mass are located at the sites of a simple cubic lattice and the potential parameters depend on elastic constants of liquid crystals. The selfconsistent equation for the molecular orientational distribution function is solved by a functional iterative method. In the bulk liquid crystals, there are three uniaxial solutions, for which the directors are along x, y and z axis respectively and the corresponding free energies are the same. A surface potential is used to describe the action of the rubbed substrate to the liquid crystal molecules, and numerical calculations are made for 5CB liquid crystal film composed of 20 molecular layers. Three states with the different directors still exist and the one with the director along the rubbed direction has the lowest free energy. In addition, the biaxial order induced by the surface action in the interface molecular layer is discussed.