Heat Capacity and Thermodynamic Properties of o-Terphenyl Crystal, Glass, and Liquid

Abstract

The heat capacity of o‐terphenyl has been measured with an adiabatic calorimeter for the crystal from 2°K to Tm (329.35°K), for the glasses from 2°K to Tg (around 240°K) and for the liquid from Tg to 360°K, on a sample with less than 0.005 mole % impurity. The heat of fusion and the entropy of fusion are 17 191 J mole−1 and 52.20 J ° K −1 · mole −1 , respectively. The residual entropy of the glasses at 0°K is about 15 J ° K −1 · mole −1 . Above 170°K, the heat capacity of the o‐terphenyl crystal is nearly proportional to the temperature to within 1%. Configurational entropy of the supercooled liquid, estimated from the result of this investigation, is used to relate the relaxation properties of glass‐forming liquids according to the theory of Adam and Gibbs. Good agreement is found for both viscosity and NMR correlation frequency data.