NONLINEARITY OF THE ENTHALPIC RESPONSE FUNCTION TO A TEMPERATURE-JUMP AND ITS INTERPRETATION BASED ON FRAGILITY IN LIQUID GLASSES

Irreversible enthalpy-relaxation processes were tracked under a constant temperature condition by the temperature jump method for liquid 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane with an adiabatic calorimeter, and simulated based on a double-well potential model with a computer. The processes were observed to show remarkable nonexponentialities and were characterized in terms of a stretched exponential function. The nonexponentiality parameter (beta) depended strongly on the magnitude of the temperature jump, indicating the nonlinearity of the relaxation processes. The results of the nonlinearity parameter (delta) combined with those of 1,2-propanediol and glycerol indicated that the nonlinearity originated primarily due to the fragility of the liquid, namely the non-Arrhenius property of the relaxation times. The degree of the nonlinearity was smaller in the endothermic processes than in the exothermic ones. The difference is discussed based on the results of a computer simulation.