Colour Switching, Dynamics and Molecular Reorientation Processes in a Very Thin Ferroelectric Liquid Crystal

Abstract

Symmetric colour switching in unaligned and aligned very thin (<1 µm) samples of ferroelectric liquid crystal DOBAMBC has been observed by applying both polarities of a dc electric field. The polarization-change current developed in a very thin FLC cell has been studied by applying symmetric (-5 V–0 V–+5 V) and asymmetric [(+ or -) 10 V–0 V] triangular wave pulses. The dynamics of colour changes amongst the same colours and amongst the multicoloured 0 V favoured state and a coloured state have been studied by applying low-voltage symmetric and asymmetric square pulses. For a symmetric triangular pulse, a single peak of polarization change and for an asymmetric pulse, two peaks of polarization change near the 0 V region for molecular reorientation amongst the same coloured state have been observed. It has been established that it is essentially the presence of an additional field, called a depolarization field, which causes a single peak of polarization-change current in the case of a symmetric pulse and it is a manifestation of the combined molecular tilt from one coloured state to another without actually attaining the multicoloured state. The switching response time corresponding to a change amongst uniform identical colours has an intermediate value between the rise and decay time for the changes amongst the 0 V favoured multicoloured state and either of the coloured states.