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.

A macroscopic model that connects the molar excess entropy of a supercooled liquid near its glass transition temperature to its viscosity Experimental evidence for excess entropy discontinuities in glass-forming solutions J. Chem. Phys. 136, 074515 (2012); 10.1063/1.3685902 Molecular relaxation and excess entropy in liquids and their connection to the structure of glass

Experimentally determined heat capacity valu es, precise to within 0.1 percent, and related thermal data are reported for quenched and annealed diethyl phthalate glasses from ]0 oK to the glass transformation te mperature, Tg (around 180 O K) , for the liquid from T" to 360 oK, and for the crystal from 10 oK to the melting temperature (269.9 O K). The mole fraction of liquid·soluble, solid·insoluble impurity in the sample as determined by fractional melting was 0.0012. Co mmon thermodynamic properties calc ulable from the experimental data are reported. The heat capacities of the two glasses differ by more than the uncertainty of the meas urements, and both lie below that of the crystal in the range from 30 to 75 oK. At low temperatures, just above 10 oK, the heat capacities of the glasses rise as much as 8 percent above that of the crystal.

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