Phase boundaries between chiral smectic C-alpha, C-beta and C phases in an antiferroelectric liquid crystal, MHPOBC

The complex dielectric constant epsilon* 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 epsilon' 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 epsilon' under DC electric field and the disappearance of the SmCalpha* phase were observed at the same optical purity. It is suggested that antiferroelectric liquid crystals are classified into two types of phase sequence: (a) -SmCbeta*-SmCalpha*-SmA-Iso, and (b)-SmC*-SmA-Iso.