PVT Measurements on 4-n-Pentyl-4´-Cyano-Biphenyl (5CB) and trans-4-(4´-Octyl-Cyclohexyl)-Benzonitrile (8PCH) up to 300 MPa

Abstract

Abstract Specific volumes are presented for 4-n-pentyl-4´-cyanobiphenyl (5CB) and trans-4-(4´-octyl-cyclo-hexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,Vm ,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,Vm ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition TNI (p) allow to determine the molecular field parameter γ = ∂In TNI /∂ In VNI.