Specific heat relaxation of an alcohol and implicationsfor dielectric comparison

摘要

The dynamic and the apparent specific heats of 5-methyl-2-hexanol were measured in itsvitrification temperature range during its cooling and then heating at the same and exceptionallyslow rates of 12 K/h and 60 K/h. The relaxation time determined from dynamic measurements is 48s at 149.8 K. The relaxation time estimated from the onset of the apparent C_p-endotherm measuredon heating is found to be inconsistent with that determined from dynamic C_p measurements. Thefitting of a nonexponential nonlinear relaxation model to the C_(p,app)data shows that βvaries slightlywith the heating rate, and this is attributed to contributions to temperature-dependent energy fromchange in the hydrogen-bond population. The unrelaxed C_pof the ultraviscous liquid is closer to thatof its glassy state, thus showing that the vibrational part of C_pdoes not increase in a sigmoid-shapemanner when the glass structure kinetically unfreezes on heating. The results have implications foruse of calorimetry in inferring the dielectric relaxation mechanism.