Light scattering spectroscopy of the liquid-glass transition: comparison with idealized and extended mode coupling theory

Abstract

Light scattering experiments were performed on several fragile glass-forming materials at temperatures ranging from above the melting temperature T, to below the calorimetric glass transition temperature T, in the frequency range 0.2 GHz to 4000 GHz. The experimental susceptibility spectra x"(o) exhibit both the form and the scaling properties predicted by the idealized mode coupling theory. In particular, the scaling frequency o, was found to obey the power law w, a 1 T -T,_jzO for three different materials, confirming the predicted "critical slowing down" as T+ Tc from either above or below. At low frequencies and temperatures the spectra deviate from the predictions due to the neglect of ergodicity-restoring activated transport (hopping) processes. We have therefore reanalyzed the data using the extended version of the theory, including activated transport.