TEMPERATURE-JUMP METHOD FOR CHARACTERIZATION OF STRUCTURAL FLUCTUATIONS AND IRREVERSIBLE RELAXATION PROCESSES IN LIQUIDS AND GLASSES

Enthalpy relaxations of propylene glycol and glycerol were followed in the time domain at 160 and 182 K, respectively, in the glass-transition region with use of an adiabatic calorimeter. The relaxation processes were analyzed and fitted with a stretched-exponential function with nonexponentiality parameter beta. Specification of the temperature jump prior to the relaxation measurement, (DELTAT)j, was found to be indispensable for the characterization of the relaxation processes in the nonlinear-response regime and the value of beta was studied as a function of (DELTAT)j. The value of beta depends on both the sign and magnitude of (DELTAT)j, indicating a characteristic difference between the rates of creation and annihilation of structurally ordered regions in liquids. However, the values of beta extrapolated from the positive and negative sides of (DELTAT)j to zero degree Kelvin agree with each other (0.62+/-0.02 for propylene glycol and 0.65+/-0.02 for glycerol, respectively), and are in excellent agreement with results obtained by heat-capacity spectroscopy. This is an experimental verification that the enthalpy-relaxational observation in time domain is equivalent to that in frequency domain only for (DELTAT)j = 0 K.