Specific heat relaxation of an alcohol and implications for dielectric comparison

The dynamic and the apparent specific heats of 5-methyl-2-hexanol were measured in its vitrification temperature range during its cooling and then heating at the same and exceptionally slow rates of 12 K/h and 60 K/h. The relaxation time determined from dynamic measurements is 48 s at 149.8 K. The relaxation time estimated from the onset of the apparent Cp-endotherm measured on heating is found to be inconsistent with that determined from dynamic Cp measurements. The fitting of a nonexponential nonlinear relaxation model to the Cp,app data shows that varies slightly with the heating rate, and this is attributed to contributions to temperature-dependent energy from change in the hydrogen-bond population. The unrelaxed Cp of the ultraviscous liquid is closer to that of its glassy state, thus showing that the vibrational part of Cp does not increase in a sigmoid-shape manner when the glass structure kinetically unfreezes on heating. The results have implications for use of calorimetry in inferring the dielectric relaxation mechanism.