Relaxational transitions and ergodicity breaking within the fluid state: The sugars fructose and galactose

We describe calorimetric and other studies of time-dependent proceses in some molecular liquid's in which there is a higher level of complexity than normally encountered in viscous liquid studies. Best characterized is the sugar D-fructose, which melts to give a liquid which is not in an equilibrium state, and in which slow relaxation processes occur in the liquid far above T-g. These have time scales up to 10 orders of magnitude longer than the shear relaxation time, yet are shown to have an important effect on the liquid viscosity and hence on the value of T-g. Three different heat capacity anomalies are identified, and are assigned to three possible tautomerization equilibria, one of which provides a major contribution to C-p and becomes slow not far below the melting point. The effects of this slow degree of freedom on liquid behaviour are discussed.