Chemistry - Biaxial nematic

A biaxial nematic is a spatially homogeneous liquid crystal with three distinct optical axes. This is to be contrasted to a simple nematic, which has a single preferred axis, around which the system is rotationally symmetric. The symmetry group of a biaxial nematic is $D 2 h$ i.e. that of a rectangular right parallelepiped, having 3 orthogonal $C 2$ axes and three orthogonal mirror planes. In a frame co-aligned with optical axes the second rank order parameter tensor of a biaxial nematic has the form

$Q= \begin{pmatrix} -\frac{1}{2}S+T & 0 &0 \\ 0 &-\frac{1}{2}S-T & 0 \\ 0 & 0& S\\ \end{pmatrix}$

where

$S$ is the standard nematic scalar order parameter

$T$ a measure of the biaxiality.

The first report of a biaxial nematic appeared in 2004 [Phys. Rev. Lett., 92, 145505 (2004)].

Categories: Crystallography