Specific heat relaxation of an alcohol and implications for dielectric comparison

Year: 2009

Authors: Tombari, E., Ferrari C., Salvetti G., Johari G.P.

Autors Affiliation: Istituto per i Processi Chimico-Fisici, CNR, Via G. Moruzzi 1, 56124 Pisa, Italy; Department of Materials Science and Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada

Abstract: 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 C(p)-endotherm measured on heating is found to be inconsistent with that determined from dynamic C(p) measurements. The fitting of a nonexponential nonlinear relaxation model to the C(p,app) data shows that beta 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 C(p) of the ultraviscous liquid is closer to that of its glassy state, thus showing that the vibrational part of C(p) 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.

Journal/Review: JOURNAL OF CHEMICAL PHYSICS

Volume: 130 (12)      Pages from: 124505  to: 124505

KeyWords: dielectric relaxation; hydrogen bonds; specific heat; vitrification;
DOI: 10.1063/1.3100188

Citations: 8
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