Specific volumes are presented for 4-n-pentyl-4'-cyanobiphenyl (5CB) and trans-4-(4'-octyl-cyclohexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,V m ,T data were determined for the liquid crystalline and isotropic phases, and partly also for the solid phase adjacent to the melting curve. Stable and metastable crystal phases can be distinguished. The density and melting temperature of the metastable form are lower than for the stable one. Volume and enthalpy changes accompanying the phase transitions are reported as well. The p,V m ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition T NI (p) allow to determine the molecular field parameter y = S In T NI /0 In F N ,.

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The phase diagram of trans-4-n-hexyl-(4'-cyanophenyl)-cyclohexane, (6PCH) has been established by high-pressure differential thermal analysis. Specific volumes are presented for temperatures between 300 and 370 K up to 300 MPa. The p,Vm ,T data have been determined for the nematic, isotropic, and (partly, in the neighbourhood to the melting curve) solid phases. Volume and enthalpy changes along the phase transitions have also been calculated. As previously, the p,Vm,T data were used to calculate the volume entropy for the nematic-isotropic transition. The molar volumes along the clearing line TNI (p) enabled us to calculate the molecular field parameter γ = ∂ln TNI/∂In VNI , being 4.1.