Collective and molecular processes in a new class of ferroelectric liquid crystals

Abstract

Electro-optic and dielectric studies have been performed for a thioester (with a chiral chain incorporating the lactic acid ester moiety), which exhibits a monotropic room temperature ferroelectric S*C phase. Moreover, there are some hints that this substance also shows the recently discovered helicoidal S*A phase. The dielectric and electro-optic measurements have been carried out using ITO coated glass plates (d = 10 μm). Planar alignment was obtained by means of an AC electric field (v = 1 Hz and VP - P = 70 V). The tilt angle and spontaneous polarization temperature dependences show that the S*A–S*C transition is of second order. Soft mode behaviour in the pretransitional region also confirms this result. The monotropic S*C phase exhibits a rather strong Goldstone mode (GM) with pronounced temperature dependence of the dielectric parameters. The molecular reorientation about the long axis has been found for both principal alignments. The homeotropic effective alignment was obtained by applying a magnetic field of 1-2T to a thick sample (c. 100 μm) placed in a specially designed cell for anisotropic high frequency measurements. The reorientation about the long axis gives a broad spectrum centred at c. 100MHz. This spectrum shows minor changes at the S*A–S*C transition. © 1995 Taylor & Francis Ltd.