Non-exponential relaxation, fictive temperatures, and dispersive kinetics in the liquid-glass-liquid transition range of acetaminophen, sulfathiazole, and their mixtures

作者：Aji D P B^*; Khouri J; Joharia G P

来源：Journal of Chemical Physics, 2014, 141(17): 174507.

DOI：10.1063/1.4901054

To investigate the effects of added molecular heterogeneity on the hysteretic features of liquid-glass-liquid transition, we studied acetaminophen, sulfathiazole, and three of their mixtures by calorimetry, and determined the T-g and the fictive temperature, T-f, from changes in the enthalpy and entropy on the cooling and heating paths, as well as the non-exponential parameter, beta(cal). We find that, (i) T-f for cooling is within 1-3 K of T-f for heating and both are close to T-g, (ii) the closed loop entropy change in the liquid-glass-liquid range is negligibly small, (iii) T-g and T-f increase on increasing sulfathiazole in the mixture, (iv) beta(cal) first slightly increases when the second component is added and then decreases, and (v) ageing causes deviations from a non-exponential, nonlinear behavior of the glass. In terms of fluctuations in a potential energy landscape, adding a solute heterogeneity would shift the state point to another part of the landscape with a different distribution of barrier heights and a different number of minima accessible to the state point. Part of the change in beta(cal) is attributed to hydrogen-bond formation between the two components. Ageing changes the relaxation times distribution, more at short relaxation times than at long relaxation times, and multiplicity of relaxation modes implied by beta(cal) %26lt; 1 indicates that each mode contributing to the enthalpy has its own T-g or T-f. beta(cal) differs from beta(age) determined from isothermal ageing, and the distribution parameter of a-relaxation times would differ from both beta(cal) and beta(age).

• 出版日期2014-11-7