Composition dependence and the nature of endothermic freezing and exothermic melting

Year: 2007

Authors: Ferrari C., Tombari E., 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, Ont. L8S 4L7, Canada

Abstract: The heat capacity, C-p, and enthalpy and entropy change of alpha-cyclodextrin, H2O, and 4-methylpyridine solutions have been studied during their freezing on heating, isothermal freezing, and the solid\’s melting on cooling. Freezing occurs in several endothermic steps on heating to 383 K and alpha-cyclodextrin rich solutions freeze in four steps. The melting rate becomes slower with decrease in temperature and its steps merge. Decreasing the amount of alpha-cyclodextrin decreases the C-p change on freezing. The endothermic freezing phenomenon differs from freezing of a pure liquid and is attributed to formation of a solid inclusion compound and its incongruent way of exothermic melting.

Journal/Review: JOURNAL OF CHEMICAL PHYSICS

Volume: 126 (12)      Pages from: 124506-1  to: 124506-4

More Information: College of Natural Resources, University of California Berkeley, CNR. – Part of this work was presented at Fifth IDMRCS meeting, 7–13 July 2005, Lille, France. One of the authors (G.P.J.) would like to thank CNR for hospitality during 2004 and 2005.
KeyWords: CYCLODEXTRIN INCLUSION COMPLEXES; HYDROGEN-BONDS; HEXAHYDRATE; CALORIMETRY;
DOI: 10.1063/1.2711179

Citations: 12
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