Freezing of capillary waves at the glass transition

Abstract

The freezing of capillary waves on glycerol surfaces is studied by in situ x-ray reflectivity measurements. A wide temperature range around the calorimetric glass transition temperature at ${T}_{g}\ensuremath{\approx}186 \mathrm{K}$ is investigated. For $T>250 \mathrm{K}$ the obtained surface roughness as a function of the temperature differs significantly from the value predicted by the classical capillary waves theory. Below the temperature $T\ensuremath{\approx}250 \mathrm{K}$ the magnitude of the roughness remains constant. Furthermore, a large hysteresis, i.e., a large difference of the roughnesses measured during cooling and heating of the sample, is observed. These findings are discussed in terms of viscosity effects.