Dielectric Relaxation in Liquid Crystal Phases with Polar Order

Abstract

Dielectric properties of a chiral smectic liquid crystal exhibiting ferroelectric and antiferroelectric forms of dipole order have been studied in the frequency range 10 Hz ÷ 1 MHz. Three relaxation bands were found in the hexatic ferroelectric phase and in the antiferroelectric phase, and six bands in the apparently ferrielectric state. The number of relaxation processes observed in the studied frequency range reduces to one in the smectic C * α and A phases. The results of measurement suggest that phases exhibiting ferrielectric properties might be in fact a mixture of ferroelectric and antiferroelectric clusters. This mixed state is stabilized by surface interactions.

Experimental evidence of soft mode in the smectic C*α phase of chiral ferroelectric liquid crystals

“…The core of our interest in the dielectric properties of the phase SmC * a was the desire to understand why does it behave more like the paraelectric SmA* phase, rather than like the ferroelectric SmC* one, as reported in numerous papers. [7][8][9][10][11][12] This is surprising, because it seems to be contrary to the expectations based on the structural analysis. In fact, it only proves that the two assumptions made in theoretical models are not exactly fullled; these can be veried by dielectric relaxation investigations:…”

“…6 According to theoretical predictions, in the smectic C * a phase, two modesthe so mode and the Goldstone one, like in the ferroelectric phase, can be observed. However, in many experimental investigations, a single collective mode is observed, [7][8][9][10][11][12] similar to the smectic A* phase. In some studies, opinion is expressed that it has an amplitude character (so mode), 7,11 while in the other ones it is considered as a phasetype Goldstone mode associated with the perturbation of the helical structure.…”