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

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.