Study of molecular dynamics of the pharmaceutically important protic ionic liquid verapamil hydrochloride. II. Test of entropic models.

In this work we analyzed the structural relaxation times as a function of both temperature and pressure in terms of the entropic models by using dielectric and PVT measurements data presented in our previous research on the ionic liquid verapamil hydrochloride [Z. Wojnarowska, M. Paluch, A. Grzybowski, et al., J. Chem. Phys. 131, 104505 (2009)]. Two different approaches were used to analyze the tau(alpha)(T,P) dependence: the modified Avramov model as well as the pressure extended Adam-Gibbs model in the forms proposed by Casalini (AG(C)) and Schwartz (AG(S)). In every case a satisfactory description of the structural relaxation times was achieved. Additionally, using both mentioned models the pressure dependence of the fragility m(P) and the glass transition temperature T(g) were determined. We also compared the value of dT(g)/dP|(P=0) calculated on the basis of the considered entropic models with the experimental value evaluated in our recent work. Consequently, we were able to estimate which of the examined models in the best way relates the dynamic to the thermodynamic parameters.