Park B, Wu J W, Takezoe H
Department of Physics, Ewha Womans University, Seoul 120-750, Korea.
Phys Rev E Stat Nonlin Soft Matter Phys. 2001 Feb;63(2 Pt 1):021707. doi: 10.1103/PhysRevE.63.021707. Epub 2001 Jan 26.
Ferroelectric ordering in a nematic liquid crystal system is described using a generalized mean-field potential including effective potentials for both axial and polar interactions. From a self-consistent numerical analysis, a complete phase diagram is obtained as a function of the axial and polar interaction potential strengths. The obtained phase diagram exhibits not only the usual isotropic-nematic phase transition but also nematic-ferroelectric nematic and direct isotropic-ferroelectric nematic phase transitions with a tricritical point among the phases. The phase transition behaviors and the angular orientational distribution function of the molecules were investigated by studying the dependence of the polar and the axial order parameters on the reduced temperature. Moreover, the other polar order parameters responsible for second-harmonic generation (SHG) were also investigated in the generalized mean-field potential description. As a concrete example, we performed a quantitative analysis of the SHG signal reported previously in a lyotropic poly L-glutamate system, detailing the relationship between the angular distribution function and the order parameters based on our potential model. This clarifies the nature of the ferroelectric phase responsible for SHG in nematics.
利用包含轴向和极性相互作用有效势的广义平均场势描述了向列型液晶系统中的铁电有序。通过自洽数值分析，得到了作为轴向和极性相互作用势强度函数的完整相图。所得到的相图不仅呈现出通常的各向同性 - 向列相转变，还呈现出向列 - 铁电向列相转变以及直接的各向同性 - 铁电向列相转变，且在这些相之间存在一个三临界点。通过研究极性和轴向序参量对约化温度的依赖性，研究了分子的相变行为和角取向分布函数。此外，在广义平均场势描述中还研究了负责二次谐波产生（SHG）的其他极性序参量。作为一个具体例子，我们对先前报道的溶致聚L - 谷氨酸系统中的SHG信号进行了定量分析，基于我们的势模型详细阐述了角分布函数与序参量之间的关系。这阐明了向列相中负责SHG的铁电相的性质。
