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_{2h} 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, the so-called Q tensor of a biaxial nematic has the form : \mathbf Q= \begin{pmatrix} -\frac{1}{2}(S+P) & 0 &0 \ 0 &-\frac{1}{2}(S-P) & 0 \ 0 & 0& S\ \end{pmatrix}

where S is the standard nematic scalar order parameter and P is a measure of the biaxiality.

The first report of a thermotropic biaxial nematic appeared in 2004

It is also found that this material can segregate into chiral domains of opposite handedness.

In one azo bent-core mesogen a thermal transition is found from a uniaxial Nu to a biaxial nematic Nb mesophase,

Another strategy towards biaxial nematics is the use of mixtures of classical rodlike mesogens and disklike discotic mesogens. The biaxial nematic phase is expected to be located below the minimum in the rod-disk phase diagram. In one study

References