Comparison between frequency-dependent specific heat and dielectric relaxation of glycerol and propylene glycol

Abstract

The recently developed technique of the frequency-dependent specific heat in the linear-response regime has given useful information on the glass transition, which is supplementary to that obtained by other techniques such as dielectric, ultrasonics, and dynamic light scattering. Previous comparisons of these spectroscopies by Birge and others have reported that the shape of the dielectric loss curves are significantly different from the specific-heat results in glycerol. This has led to speculation of the existence of modes of relaxation that carry entropy but have a very small dipole moment. In this work, we analyze the original glycerol dielectric relaxation data of Howell as well as the dielectric results of Davidson and Cole. We find that the dielectric and specific-heat results for glycerol are in reasonable agreement for both the fractional exponent β of the Kohlrausch-Williams-Watts function and the temperature dependence of loss peak frequencies. The analysis has also been carried out for propylene glycol. However, in this case we find a difference in the values of β for the dielectric and specific-heat results. The dielectric loss peaks are significantly narrower than the peaks from specific-heat spectroscopy.