Numerical study of deformations induced by ac electric field in insulating flexoelectric nematic layers

Abstract

The influence of the frequency f of applied ac electric field on the time dependence of electric field induced deformations of homeotropic nematic layers is studied numerically. Three kinds of nematic liquid crystals were considered: non-flexoelectric nematic with negative dielectric anisotropy, Δɛ < 0dielectrically compensated nematic (Δɛ = 0) possessing flexoelectric properties determined by the positive sum of flexoelectric coefficients e = e11 + e33 > 0nematic characterised by both Δɛ < 0 and e > 0.It was found that at sufficiently low frequencies, the deformations varied with time. The deformations of purely dielectric nature had the period 1/(2f). When the frequency was increased, a stationary director distribution was achieved, determined by the rms value of the ac voltage. The time period of purely flexoelectric distortions was equal to 1/f. There was a well defined cut-off frequency above which these deformations vanished. In the case of dielectrically anisotropic and flexoelectric nematic, the flexoelectric contribution vanished above a critical frequency and the deformation of dielectric nature stabilized at high frequencies.

Role of flexoelectricity in electro-optical properties of hybrid aligned nematic layers

“…If the AC voltage of sufficiently high frequency is applied, the sign and magnitude of the flexoelectric torques vary with the same frequency but viscosity of the nematic liquid prevents any fast rotations of the director, i.e., the flexoelectric contribution to director distribution vanishes. 2 The dielectric torques vary with doubled frequency, but they do not change their sign; therefore, they do not induce reorientation of the director and the viscous torques do not frustrate their action, but only damp possible small oscillations. As a result, the static director distributions in the AC field of sufficiently high frequency are induced solely by the dielectric interactions and depend on the root mean square of the bias voltage.…”