Calorimetric and dielectric investigations of the phase transformations and glass transition of triphenyl phosphite

The phase transformations and the glass-liquid transition on heating of supercooled Liquid triphenyl phosphite (TPP) were studied by differential scanning calorimetry and fixed frequency dielectrometry, and the nature of its various states was discussed. The dielectric behavior of the so-called ''glacial'' phase shows that the slow rise in its apparent heat capacity on heating is a reflection of its exceptionally broad glass-softening transition, due to a multiplicity of relaxation times, and not its premelting. The static permittivity near its freezing point is 3.6, and the change in both the permittivity and loss shows the temperature range of the supercooled liquid --> ''glacial'' --> crystal --> liquid phase transformations. These transformations are illustrated by the free energy plots, and calorimetry was done to determine their merits. The heat capacity of the glass is comparable with that of the crystal phase, which indicates that the anharmonic phonon contributions to C-p in the glass and crystal phase are comparable, but that of the glacial phase is more than that of both the glass and crystal phases. In its thermal and dielectric manifestations, the ''glacial'' phase appears to be similar to an orientationally disordered crystal formed by a first-order transformation of a supercooled metastable liquid such as ethanol, but fails to reveal whether or not that phase is of liquid-crystal type.