G. Blond

Modeling of the water-sucrose state diagram below 0 °C

The state diagram of sucrose-water solutions was constructed by the use of model calculations; the activity coefficient from the UNIQUAC model allowed determination of the solution-ice equilibrium curve and the glass transition temperature as a function of the composition was evaluated from the Gordon-Taylor equation. The accuracy of the glass transition temperature (T′g) of the maximally freeze-concentrated fraction, determined from the intersection of both curves, was analyzed and discussed. While the UNIQUAC model predicted reliable ice melting temperatures in the high sucrose concentration range, a significant variation of the fitted glass transition curve was obtained due to the selected temperature values for the glass transition temperature. The calculated glass temperatures (T′g) were compared with direct DSC experiments. While the UNIQUAC model predicted reliable ice melting temperatures in the high sucrose concentration range, a significant variation of the fitted glass transition curve was obtained due to the selected temperature values as the glass transition temperature. The calculated glass temperatures (Tg′ were compared with direct DSC experiments.

Glass transition of the amorphous phase in frozen aqueous systems

Abstract Thermal analysis can be successfully used for studying the enthalpy of complex glass transitions. The comparison of the incremental change in heat capacity in the glass transition temperature range for glassy or freeze-concentrated systems had indicated a large discrepancy. Theoretical calculations of heat capacity change in solid-liquid transitions show that the complex events observed in freeze-concentrated materials might be considered as the appearance of the glass transition of their amorphous fraction.

Optimized thermal treatments to obtain reproducible DSC thermograms with sucrose + dextran frozen solutions

Abstract The freezing behaviour of concentrated model solutions has been studied by differential scanning calorimetry (DSC) over a large range of sucrose + dextran ratios. When conventional thermal cycles (10 °C/min) are used, it is observed that the freezing is depen- dent on the dextran concentration, i.e. the amount of unfrozen water increases with the dextran concentration.The high viscosity of the concentrated solution limits the ice crystal growth during the cooling step of the DSC analysis. In order to obtain maximally freeze-concentrated samples, a methodology is proposed that corresponds to specific annealing treatments