Dielectric evidence of an electroclinic effect in the cholesteric phase near a N * -SmA-SmC * multicritical point

Abstract

Chiral liquid crystal materials (n = 10 and 11 homologues of a biphenyl alkyloxybenzoate series) exhibiting the ferroelectric smectic C phase (SmC*), the smectic A phase (SmA) and the cholesteric phase (N*) have been studied by structural, electro-optical and dielectric methods. In the structural study, helical pitch, tilt angle and polarization measurements show that the N* -SmC* and the N* -SmA phase transitions appear near a N* -SmA-SmC* multicritical point. In the dielectric measurements, we have studied the soft mode in the SmC* and SmA phases. We have detected a new relaxation mechanism in the N* phase of these compounds. The temperature dependence of this relaxation process is similar to that of the classical soft mode observed in the SmA phase. This dielectric relaxation process is attributed to an electroclinic effect in the N* phase near a N*-SmA-SmC* multicritical point. From the experimental data (structural and dielectric studies), we have evaluated the soft mode rotational viscosity, the α -coefficient of the free energy and the electroclinic coefficient for the SmA and N* phases.