The influence of chirality and dielectric anisotropy on the voltage-temperature phase diagram of blue-phase systems

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Abstract
Voltage-temperature phase diagrams of liquid-crystalline blue-phase (BP) systems have been determined by means of polarizing microscopy and Bragg reflection spectroscopy. A three-component system composed of two non-chiral nematics with Δϵ > 0 and Δϵ < 0, and one chiral nematic with Δϵ ≊ 0 has been studied, which allows the independent variation of chirality and dielectric anisotropy (Δϵ) over wide ranges. Mixtures of positive and negative resultant dielectric anisotropy have been investigated. They exhibit up to three zero-field BPs: BPI, BPII and BPIII (fog phase). Besides field-induced BP to cholesteric transitions, several field-induced BPs have been detected that are unstable in the field-off state. The effect of chirality and dielectric anisotropy on the transition temperature and the transition field strengths are evaluated, as well as the conditions for the occurrence of the field-induced BPs.