液晶SmC相螺旋结构的统计理论

STATISTICAL THEORY OF HELICAL STRUCTURE IN SmC~* LIQUID CRYSTALS

采用格胞模型,定义在格胞中心上的分子取向序参量、质心位置序参量和两者耦合序参量。选用双轴性并有横向电偶极矩的分子的作用两体势,求出系统的自由能,对自由能求变分得到指向矢满足的微分方程,由此方程得到SmC相指向矢与分子层面法线倾斜,并沿该法线作螺旋式变化,求得倾斜角和螺距的近似表示式,计算了DOBAMBC等三种典型SmC相液晶的倾斜角和螺距随温度的变化,结果与实验相符。

With cell model, the orientional order parameter, the positional order parameter and the orien-tion and position coupling order parameter are defined on cell center. By choice of interaction potential of biaxial molecules with a permanent electric dipole moment transverse to the molecular long axis, the free energy of the system is obtained . A differential equation of the director is derived by calculating the variation with respect to free energy, and the director tilt and helical change about the normal of molecular layer are obtained. The approximate formulas of tilt angle and pitch for three classic SmC* Liquid crystals of DOBAMBC, etc., are presented. The calculated results agree satis-factorily with the experimental ones.