CALORIMETRIC CHARACTERIZATION AND COMPUTER-SIMULATION, BASED ON A THERMAL-ACTIVATION MODEL, OF IRREVERSIBLE STRUCTURAL RELAXATION PROCESSES IN LIQUID DIBUTYLPHTHALATE

The irreversible enthalpy relaxation processes in liquid dibutylphthalate were tracked under constant-temperature conditions by the temperature jump method with an adiabatic calorimeter, and the relaxation functions were characterized in terms of the stretched exponential function with a nonexponentiality parameter, beta. Remarkable nonlinearity, delta, of the relaxation functions with the magnitude of temperature jump, Delta(j)T, was found, and reasonably interpreted to be due to the fragility, m, of the liquid from the comparison with the result of computer simulation based on a thermal activation model for the microscopic rearrangement of molecules. The validity of the Tool-Narayanaswamy model is also discussed on the basis, of the simulation result.