Ribeiro Mauro C C, Scopigno Tullio, Ruocco Giancarlo
Laboratório de Espectroscopia Molecular, Instituto de Química, Universidade de São Paulo, C.P. 26077, 05513-970 São Paulo, SP, Brazil.
J Phys Chem B. 2009 Mar 12;113(10):3099-104. doi: 10.1021/jp810934e.
The pressure dependence of the glass-transition temperature, Tg(P), of the ionic glass-former 2Ca(NO3)2 x 3KNO3, CKN, has been obtained by molecular dynamics (MD) simulations The liquid-glass difference of thermal expansivity, deltaalpha, heat capacity, deltaCp, and isothermal compressibility, deltak, have been calculated as a function of pressure. It has been found that the Ehrenfest relation dTg/dP = TVdeltaalpha/deltaCp predicts the pressure dependence of Tg, but the other Ehrenfest relation, dTg/dP = deltakappa/deltaalpha, does not. Consequently, the Prigogine-Defay ratio, pi = deltaCpdeltakappa/TVdeltaalpha2, is n pi approximately 1.2 at low pressures, but increases 1 order of magnitude at high pressures. The pressure dependence of the Prigogine-Defay ratio is interpreted in light of recent explanations for the finding pi > 1.
