Experimental Study on Solid-Liquid and Liquid-Liquid Phase Equilibria under High Pressure

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The solid-liquid (SLE) and liquid-liquid (LLE) phase equilibria have been investigated experimentally for the following binary or ternary systems : 1) (Benzene, Cyclohexane + n-Ttetradecane, n-Hexadecane), 2) (Benzene + Cyclohexane + n-Tetradecane), 3) (MBBA (N-4-methoxybenzylidene-4'-n-butylaniline) + EBBA (N-4-ethoxybenzylidene-4'-n-butylaniline), 4) (MBBA,EBBA + Benzene, Cyclohexane) at temperatures from 230 to 363 K and pressures up to 120 MPa. The measurements of the phase transitions were performed using high pressure optical vessels designed for visual observation with the aid of a video microscope, and a three-terminal cylindrical capacitor designed for dielectric permittivity measurement. Concerning 1) and 2), the SLE diagrams of the investigated systems consist of two liquidus curves intersecting at a eutectic point. The solid-liquid coexistence curve and the eutectic point are found to increase to higher temperatures monotonically with increasing pressure in each system. The … More SLE diagrams at atmospheric pressure could be predicted successfully by the UNIF AC estimation method.Concerning the phase equilibria in binay liquid crystalline systems, the items 3) and 4), the crystal-nematic (T_<CN>) and nematic-isotropic (T_<NI>) transition temperatures were measured. A eutectic is found in the T_<CN> transition at a mole feaction of EBBA 0.2 and a temperature of 284 K in (MBBA + EBBA) system at atmospheric pressure. The T_<NI> transition temperatures are linear with respect to the composition of EBBA.Both transition temperatures T_<CN> and T_<NI> shift to higher temperature linearly with increasing pressure. In (MBBA,EBBA + Benzene, Cyclohexane) systems, the T_<CN> transition temperature decreases gradually with the concentration of isotropic components at atmospheric pressure. On the other hand, T_<NI> decreases remarkably with the addition of isotropic component up to 0.3-0.4 mole fraction. Addition of nonpolar isotropic component may give rise to serious effect to the packing of molecules and molecular interaction in the liquid crystals. Less