Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Calorimetric Study of the Glassy State. VIII. Heat Capacity and Relaxational Phenomena of Isopropylbenzene
Koji KishimotoHiroshi SugaSyûzô Seki
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1973 Volume 46 Issue 10 Pages 3020-3031

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Abstract

The heat capacities of isopropylbenzene were measured with an adiabatic calorimeter for the crystal from 14 to 177.13 K (Tm), for the glassy state from 14 to around 126 K (glass transition temperature: Tg) and for the liquid from Tg to 313 K, with a sample of 99.93% purity. The heat and entropy of fusion were found to be 7326 J mol−1 and 41.36 J K−1 mol−1, respectively. Based on these data, a set of thermodynamic functions are tabulated at rounded temperatures. In addition to the primary glass transition phenomenon, a secondary enthalpy relaxation as well as a step-like heat capacity anomaly was observed at around 70 K. These facts were discussed in correlation with the β-relaxation already observed by dielectric measurement. Gonfigurational entropies of the supercooled liquid and of the glassy state were calculated to investigate a relation with relaxational properties. The agreement is found between the temperatures where catastrophe occurs in viscosity (T0), and where the configurational entropy vanishes (T2). Finally, a kind of heat capacity break observed in the liquid state is discussed against the view that this behavior is compatible with a third-order thermodynamic transition.

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