Phase transitions and conformational changes in an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC)

Abstract

The thermodynamic properties and conformational structures in the crystalline and liquid crystalline phases of 4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC) have been investigated by Raman scattering, X-ray diffraction and differential scanning calorimetry (DSC). MHPOBC can assume two different crystalline states at room temperature depending on crystallization conditions, and heating transforms the metastable crystal to the stable one before melting. In the liquid crystalline phases, Raman scattering spectra have revealed not only the flip-flop twisting vibration of the biphenyl group but also the internal rotation around C-C bonds between the carbonyl groups and the corresponding benzene rings.