Light-scattering investigation of α and β relaxation near the liquid-glass transition of the molecular glass Salol

Abstract

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 ${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}256 K which is about 40 K above the glass-transition temperature ${\mathit{T}}_{\mathit{g}}$. The \ensuremath{\beta}-relaxation process is well described by the scaling predictions of the mode-coupling theory in both the liquid and glass states. The \ensuremath{\alpha} relaxation obeys the time-temperature superposition principle for T>${\mathit{T}}_{\mathit{c}}$. The light-scattering results, when combined with previous dielectric measurements, indicate a continuous evolution of the relaxation time and stretching of the \ensuremath{\alpha} 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.