Effects of Pressure on Dielectric Relaxation in Supercooled Triphenylchloromethane–<i>o</i>-Terphenyl Solution

Abstract

Abstract Dielectric measurements have been made as a function of frequency, temperature, and pressure on a binary mixture of triphenylchloromethane and o-terphenyl in its supercooled liquid region. Since the distribution of relaxation time is independent of temperature and pressure in the present experimental range, the time-temperature-pressure superposition is accurately applied. The activation parameters such as the activation enthalpy at constant pressure, H*P, the activation enthalpy at constant volume, H*V, and the activation volume V* are obtained as a function of temperature and pressure. H*V is only half H*P unlike liquids and associated liquids such as alcohols. V* as well as the pressure coefficient of temperature at constant relaxation time τ, (∂T⁄∂T)τ, is similar in magnitude to that of polymer liquids and larger than that of associated liquids. These facts have revealed the contributions of inter- and intramolecular interactions to the molecular mobility in the supercooled liquid. (∂T⁄∂P)τ coincides with the pressure coefficient of the glass transition temperature, dTg/dP. This gives a statement that the glass transition temperature in simple normal liquids, as well as in polymer liquids, is an isorelaxation-time state.