Complementary Method of Assessment of Frank Elastic Constants in Nematic Liquid Crystals

Abstract

new method for quick and accurate measurements of splay (S), twist (T) and bend (B) elastic constants of nematic liquid crystals (NLC) is proposed. The main concept relies on utilizing an electric field only and on determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in a single, hybrid, In-Plane-Switched (IPS) cell. In Hybrid In-Plane-Switched (HIPS) cell, the deformations of an investigated LC are optically monitored while driven by three separated pairs of electrodes. Two of them are interdigitating ones. Due to the appropriate IPS electrodes and boundary conditions on them, the splay, twist and bend elastic constants can be measured without allaying the magnetic field. In this chapter, we describe the layout of HIPS measuring cells and the results of tests conducted on them using 5CB, 6CHBT (with Δε > 0) and DE (with Δε < 0).

Keywords: Homeotropic alignment, Homogeneous alignment, In-plane-switched cell, Nematic liquid crystals, Optical anisotropy, Permeability anisotropy, Permittivity, Refractive indices, Splay, Threshold voltages.