Flexoelectric and dielectric in-plane switching behaviour of Grandjean liquid-crystal structures

A key requirement for the exploitation of the chiral-flexoelectrooptic effect in technology is the development of materials with large flexoelectric response and small dielectric anisotropy. Consequently, techniques to understand details of the switching of chiral systems used in such technologies require development. Here, analytical and numerical models of dielectric and flexoelectric switching in cholesteric liquid-crystal structures with in-plane switching (IPS) electric fields are employed to analyse angle-of-incidence–dependent transmission of Grandjean structures. Adoption of a perturbative driving regime, and measurement of both 1st- and 2nd-harmonic transmission amplitudes, allow the detailed and simultaneous measurement of distortions arising from both flexoelectric and dielectric interactions, at electric fields as little as 0.01 Vμm−1. The method is applied to measure the flexoelectric parameter (e1 − e3)/(K1 + K3) and the dielectric distortion parameter Δε/K2 in E7 liquid crystal and a bimesogen mixture MDA-1245 optimised for the chiral-flexoelectrooptic effect