Elastic constants of nematic liquid crystals of uniaxial symmetry

TL;DR

This paper investigates how molecular interactions influence the elastic constants of uniaxial nematic liquid crystals, combining theoretical models with numerical calculations for specific systems and comparing results with experimental data.

Contribution

It provides a detailed numerical analysis of the effects of repulsive and attractive interactions on elastic constants, improving understanding of molecular influence in nematic liquid crystals.

Findings

Quadrupole and dispersion interactions have minor effects compared to repulsive interactions.

Including attractive interactions decreases elastic constant ratios.

Theoretical results show good agreement with experimental data.

Abstract

We study in detail the influence of molecular interactions on the Frank elastic constants of uniaxial nematic liquid crystals composed of molecules of cylindrical symmetry. A brief summary of the status of theoretical development for the elastic constants of nematics is presented. Considering a pair potential having both repulsive and attractive parts numerical calculations are reported for three systems MBBA, PAA and 8OCB. For these systems the length-to-width ratio ${x_0}$ is estimated from the experimentally proposed structure of the molecules. The repulsive interaction is represented by a repulsion between hard ellipsoids of revolution (HER) and the attractive potential is represented by the quadrupole and dispersion interactions. From the numerical results we observe that in the density range of nematics the contribution of the quadrupole and dispersion interactions are small as compared to the repulsive HER interaction. The inclusion of attractive interaction reduces the values of elastic constants ratios. The temperature variation of elastic constants ratios are reported and compared with the experimental values. A reasonably good agreement between theory and experiment is observed.