Heat Release from a Supercooled Liquid near Glass Transition

We have studied by a novel experiment, the heat release from supercooled liquids (glycerol and propylene glycol) as these liquids cool below the glass transition temperature $(T_g)$ through a thermal link of defined heat loss. We find that the cooling rate as a function of temperature shows two kinds of behaviour. In well-annealed samples, the observed cooling rate can be explained by the temperature dependence of the structural relaxation time and is independent of the thermal history of the sample. On the other hand, we find that a glass warmed up to $T>T_g$ and recooled without annealing shows an anomalous feature in the cooling rate which is strongly dependent on the thermal history and which cannot be explained by the structural relaxation time alone