DIFFERENTIAL THERMAL-ANALYSIS (DTA) UNDER HIGH-PRESSURE .6. PHASE-TRANSITIONS OF SOME LIQUID-CRYSTALS UP TO 3-KBAR

The phase transition temperature solid/nematic (melting temperatures) and nematic/liquid isotropic (clearing temperatures) of the liquid crystals MBBA, EBBA, PBBA, PEBAB, PAA, and PAP were measured as a function of pressure up to 3 kbar and in the temperature range 273 K to 550 K. For PBBA the pressure dependence of the transition temperature smectic/nematic was additionally determined. For all compounds arising pressure causes an increase of the transition temperatures as well as an extension of the nematic range (especially for PAA and PEBAB). According to the thermal pretreatment two different melting curves were found for MBBA, EBBA and PEBAB separating the nematic liquid from a stable and a metastable solid phase repectively. The melting curves diverge slightly for MBBA and EBBA; for PEBAB, however, an intersection point can be extrapolated at about 2600 bar and 450 K.