Isothermal high-pressure studies of 4-cyano-3-fluorophenyl 4-butylbenzoate dynamics near room temperature

Abstract

For 4-cyano-3-fluorophenyl 4-butylbenzoate, a glass former giving glass of nematic phase at ambient pressure and after rapid pressurizing, isothermal studies of complex dielectric permittivity vs pressure were performed near room temperature. In the previous isobaric experiment, on cooling the nematic phase two super-Arrhenius α relaxations, ascribed to the reorientations of molecules around short axes (main process) and precession of long molecular axes, and β relaxation related to intramolecular motions were found. In the present isothermal experiments nematic-smectic phase transition was induced by increasing pressure. Linear pressure dependence of the logarithm of the dielectric relaxation time gives activation volume of about 70 cm(3)/mole for liquid crystalline phases and 50 cm(3)/mole for the isotropic phase. The time-temperature-pressure superposition principle for the α-relaxation process was found to be valid (i.e., a single master curve can be obtained by superpositioning dielectric loss curves measured at various temperatures and pressures).