Influence of the proximity of a N*–SmA–SmC* multicritical point on the electroclinic effect in the cholesteric phase

Abstract

Chiral liquid crystal material (C12 homologue of biphenyl benzoate series) exhibiting the cholesteric (N*), smectic A (SmA) and ferroelectric smectic C (SmC*) phases have been studied by structural, thermodynamic, electrooptical and dielectric investigations. The helical pitch, tilt angle and spontaneous polarization have been determined. In the dielectric measurements, we have studied the soft mode in the SmC* and SmA phases. From experimental data, we have evaluated the soft‐mode rotational viscosity and the electroclinic coefficient in the SmA phase. All results are discussed and compared with previous studies performed on other homologues of the same series. The main result is that the relaxation process detected in the N* phase for the C8, C10 and C11 homologues and explained as a soft‐mode‐like mechanism, is not observed for C12. This corroborates the idea that this mechanism is related to the appearance of smectic order fluctuations within N* phase, the amplitude of which is increased when approaching the SmC*–SmA–N* multicritical point.