Phase Boundaries between Chiral Smectic C_α, C_β and C Phases in an Antiferroelectric Liquid Crystal, MHPOBC

Abstract

The complex dielectric constant ε * of 4-(1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) was measured as a function of temperature, optical purity and DC electric field, and switching current behavior was observed as a function of temperature and optical purity. A two-step change in the real part of complex dielectric constant ε ′ with DC electric field and several peaks in switching current were observed in high optical purity samples, but not in low optical purity ones. The phase diagram of temperature versus optical purity was obtained from the results. The disappearance of the two-step decrease in ε ′ under DC electric field and the disappearance of the SmC α * phase were observed at the same optical purity. It is suggested that antiferroelectric liquid crystals are classified into two types of phase sequence: (a) –SmC β * –SmC α * –SmA–Iso. and (b) –SmC * –SmA–Iso.