Structural and entropic modes in supercooled liquids: experimental andtheoretical investigation

Abstract

We studied the relaxation processes of glycerol by a transient grating experimentwith polarization selectivity and optical heterodyne detection. The densityresponse of supercooled glycerol, for a wavevector q = 0.63 μm−1,has been studied in that temperature range (T = 200– 340 K),where the rearrangement of the structure (α-relaxation)and thermal diffusion occur on the same timescale. A strong interactionbetween the two modes is observed, manifesting in a dip in theT dependenceof the apparent thermal conductivity and in a flattening of the apparent α-relaxationtime upon cooling. A parameter-free thermo-hydrodynamic model for thelong-time response is developed. The model is capable of quantitativelyreproducing the data and of explaining the observed phenomenology.