Phase Transitions in an Antiferroelectric Liquid Crystal TFMHPOBC

Abstract

We studied phase transitions in an antiferroelectric liquid crystal TFMHPOBC (C 8 H 17 O-&benzf;-&benzf;-COO-&benzf;- * CH(CF 3 )C 6 H 13 ) by means of dielectric measurements and microscopic observations. Both a Goldstone mode and a soft mode were observed in the SmC * phase, but only a soft mode in the SmC A * phase. From the temperature dependence of the relaxational frequency, it was clarified that the ferroelectric mode tends to be soft even in the antiferroelectric phase transition. The unwinding process of the helical structure in the SmC A * phase was observed with a reflecting microscope. It was also found that all the transitions, i.e., SmA-SmC A * , SmA-SmC * and SmC * -SmC A * , are of the first order. We present the E(electric field)-T(temperature) phase diagram of the optically pure TFMHPOBC and the mixture of R- and S-enantiomers.