Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, UK.
J Phys Condens Matter. 2010 Sep 15;22(36):362101. doi: 10.1088/0953-8984/22/36/362101. Epub 2010 Aug 11.
Order parameters and phenomenological theory for both high- and low-symmetry biaxial nematic phases are presented and it is predicted that the chiral low-symmetry biaxial phase must be ferroelectric. This conclusion is based on general symmetry arguments and on the results of the Landau-de Gennes theory. The microscopic mechanism of the ferroelectric ordering in this chiral biaxial phase is illustrated using a simple molecular model based on dispersion interactions between biaxial molecules of low symmetry. Similar to the chiral smectic C* phase, the ferroelectricity in the chiral biaxial nematic phase is improper, i.e., polarization is not a primary order parameter and is not determined by dipolar interactions. Ferroelectric ordering in biaxial nematics may be found, in principle, in materials composed of chiral analogues of the tetrapod molecules which are known to exhibit biaxial phases.
呈现了高对称和低对称双轴向列相的序参量和唯象理论，并预测手性低对称双轴相一定具有铁电性。这一结论基于一般的对称论证和朗道-德热纳理论的结果。通过基于低对称双轴分子之间的色散相互作用的简单分子模型，说明了这种手性双轴相中铁电有序的微观机制。与手性近晶 C*相类似，手性双轴向列相的铁电性是不合适的，即极化不是主要序参量，也不由偶极相互作用决定。在原则上，在由已知表现出双轴相的四足分子的手性类似物组成的材料中可以发现双轴向列相的铁电有序。
