PVT measurements on n -octyl-isothiocyanato-biphenyl (8BT) at elevated pressures

Abstract

For the first time pressure-volume-temperature (PVT) measurements for the crystal-like smectic E phase have been performed. The phase diagram of 4′-n -octyl-4-isothiocyanatobiphenyl 8BT has been recently established using differential thermal analysis up to 250 MPa. 8BT exhibits a splitting of the clearing line above 170 MPa. PVT data have been measured in the same pressure range for temperatures between 313 and 393 K. Volume and enthalpy changes accompanying the clearing line of 8BT are also presented. The configurational part of the entropy change at the CrE-I transition of 8BT amounts to ≈ 60%. Using the PVT data and recently published dielectric relaxation results, the isochoric activation energy was calculated (giving ≈ 50% of the activation enthalpy); this is compared with analogous results for other liquid crystals.