LIGHT-SCATTERING INVESTIGATION OF ALPHA-RELAXATION AND BETA-RELAXATION NEAR THE LIQUID-GLASS TRANSITION OF THE MOLECULAR GLASS SALOL

The liquid-glass transition dynamics of the molecular glass Salol has been studied by light-scattering spectroscopy from 383 to 198 K. Analysis of wide-frequency-range composite spectra revealed the relaxation dynamics from 0.2 GHz to 3.5 THz. A two-step relaxation process was observed near the crossover temperature T(c) is similar to 256 K which is about 40 K above the calorimetric glass-transition temperature T(g). The beta-relaxation process is well described by the scaling predictions of the mode-coupling theory in both the liquid and glass states. The alpha relaxation obeys the time-temperature superposition principle for T > T(c). The light-scattering results, when combined with previous dielectric measurements, indicate a continuous evolution of the relaxation time and stretching of the a process from the liquid to the glass state. Qualitative and quantitative comparisons of the experimental results with the predictions of the mode-coupling theory and the configuration-space percolation theory are presented.