Ferroelectric and electroclinic characterisation of a new organic siloxane bimesogen

Abstract

A new siloxane based twin dimer has been synthesised which exhibits both a broad ferroelectric phase (from sub ambient temperatures to 37.5°C), and a Sa phase extending over 12.5°C (from 37.5°C to 50°C). The electroclinic effect within the Sa phase is very pronounced, occurs throughout the Sa phase and exhibits electroclinic coefficients as large as 2°/Vrms/μm at a temperature of Tsc*/Sa^+5°C. The response times are correspondingly low (as little as 25μs at the end of the Sa range) and the maximum induced tilt angles very large, up to 17° at TSc*/sa^+6°C and even higher closer to the phase transition. The effect of the soft mode contribution to the measured tilt angle can be seen far back into the ferroelectric phase. Characterisation has been performed by electro optic analysis, X ray studies, textural observations and measurement of spontaneous polarisation.