Electric Field Induced Phase Transitions and Colour Switching in the Blue Phases of Chiral Nematic Liquid Crystals

Abstract

The phase behavior and electro-optic phenomena observed in a new system of blue phase mixtures have been determined. The mixtures, which include both cyanobiphenyl and chiral ester components, have relatively high pitch values (∼0.3 μm) but nonetheless exhibit broad blue phase temperature ranges (∼2.5°C total). On application of electric fields to samples of these materials, colour switches and phase transitions to both turbulent chiral nematic and homeotropic nematic states were induced in both BPI and BPII. Both of these electric field induced phenomena are described as functions of the applied voltage and frequency. The response times of these field effects were also determined with high accuracy and found in the case of the field transitions to be extremely fast (∼100 μs). The mechanism associated with the field induced colour switch was found to have two distinct response times associated with it, one fast (∼100 μs) and the second much slower (∼1–10 μs). Finally, the relaxation phenomena observed for each of these field effects in BPI and BPII are described. These relaxation mechanisms give evidence supporting the belief that the structure of the fog phase (BPIII) is linked to that of BPII.