Vibrational and configurational parts of the specific heat at glass formation

Year: 2008

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

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

Abstract: The specific heat C-p of a liquid is partly vibrational, arising from change in phonons and anharmonic forces with temperature T, and partly configurational, arising from change in the structure with T. The first determines a liquid’s elastic resistance to stress or rigidity and the second its fluid behavior. Both are thought to decrease on liquid’s vitrification, and their ad hoc estimates are currently used for understanding a supercooled liquid’s dynamics. We report measurements of the vibrational part, C-p,C-vib, and determine the configurational part. It is found that there is almost no decrease in C-p,C-vib on structural freezing of the polymer melts, and the decrease in C-p is configurational. An interpretation of the finding is that the curvature of the fixed configurational energy minimum in which a polymer glass structure is trapped and the associated anharmonicity have quantitatively the same effect on C-p as the corresponding two sources when its melt explores a multiplicity of high energy minima and its volume changes.


Volume: 77 (2)      Pages from: 024304  to: 024304

DOI: 10.1103/PhysRevB.77.024304

Citations: 19
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