PHASE-TRANSITIONS AND CONFORMATIONAL-CHANGES IN AN ANTIFERROELECTRIC LIQUID-CRYSTAL 4-(1-METHYLHEPTYLOXYCARBONYL)PHENYL 4'-OCTYLOXYBIPHENYL-4-CARBOXYLATE (MHPOBC)

The thermodynamic properties and conformational structures in the crys talline and liquid crystalline phases of 4-(1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) have been investigat ed by Raman scattering, X-ray diffraction and differential scanning ca lorimetry (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. I n the liquid crystalline phases, Raman scattering spectra have reveale d not only the flip-flop twisting vibration of the biphenyl group but also the internal rotation around C-C bonds between the carbonyl group s and the corresponding benzene rings.