COLLECTIVE AND MOLECULAR PROCESSES IN A NEW CLASS OF FERROELECTRIC LIQUID-CRYSTALS

Electro-optic and dielectric studies have been performed for a thioest er (with a chiral chain incorporating the lactic acid ester moiety), w hich exhibits a monotropic room temperature ferroelectric S(C)phase. Moreover, there are some hints that this substance also shows the rece ntly discovered helicoidal S(A) phase. The dielectric and electro-opt ic measurements have been carried out using ITO coated glass plates (d = 10 mum). Planar alignment was obtained by means of an AC electric f ield (nu = 1 Hz and V(p-p) = 70 V). The tilt angle and spontaneous pol arization temperature dependences show that the S(A)-S(C)* transition is second order. Soft mode behaviour in the pretransitional region al so confirms this results. 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 eff ective alignment was obtained by applying a magnetic field of 1.2T to a thick sample (c. 100 mum) placed in a specially designed cell for an isotropic high frequency measurements. The reorientation about the lon g axis gives a broad spectrum centred at c. 100 MHz. This spectrum sho ws minor changes at the S(A)-S(C)* transition.