Dielectric relaxation in chevron surface stabilized ferroelectric liquid crystals

TL;DR

This study investigates the dielectric relaxation behavior of chevron-structured surface stabilized ferroelectric liquid crystals, revealing two Debye relaxation processes at medium frequencies and complex wall dynamics at various electric field strengths.

Contribution

It provides an analytical and experimental analysis of dielectric relaxation and zigzag wall dynamics in chevron ferroelectric liquid crystals, highlighting multiple relaxation processes and wall motions.

Findings

Identification of two Debye relaxation processes linked to chevron slabs.

Experimental confirmation of relaxation processes using electro-optic techniques.

Observation of three types of zigzag wall motions affecting electro-optic response.

Abstract

The dielectric response of surface stabilized ferroelectric liquid crystals with chevron layer structure is studied within low and intermediate frequency ranges, characteristic for collective molecular excitations. By analytically solving the dynamic equation for collective molecular fluctuations under a weak alternating electric field, it is demonstrated that chevron cells stabilized by both nonpolar and polar surface interactions undergo at medium frequencies two Debye relaxation processes, connected with two chevron slabs, on opposite sides of the interface plane. This result is confirmed, experimentally, making use of the electro-optic technique. Based on qualitative arguments supported by microscopic observations of zigzag defects at different frequencies and amplitudes of the external electric field, it is shown that, at low frequencies, the electro-optic response of chevron samples is determined by three kinds of motions of zigzag walls. The first two dynamic categories are related to collective relaxation processes at weak fields, within smectic A layers forming zigzag walls, and drift or creep motions of thick walls occuring at stronger field amplitudes. Dynamic processes of the third kind correspond to sliding of zigzag walls, which appear at yet stronger field amplitudes, but below the switching threshold.