Eutectic mixtures for pharmaceutical applications: A thermodynamic and kinetic study

The thermodynamics and kinetics of the solidification process of several mixtures of SR 33557 and PEG 6000 have been analyzed by differential scanning calorimetry. The calculated phase diagram showed a negative interaction energy between the constituents in the liquid phase. A unified description for solidification accounting for isothermal and continuous cooling is resented. The onset of solidification shifts to higher temperatures on decreasing the cooling rate and to longer times on decreasing the annealing temperature under continuous cooling and isothermal holding, respectively. The analysis is based on the fact that nuclei have to be created prior to any crystal growth. The driving force for nucleation is considered proportional to the undercooling, Delta T(= T-L - T). By coupling the isothermal and continuous cooling experiments, the high temperature part of the time-temperature transformation and temperature-cooling rate transformation diagrams are constructed under a wide range of conditions. (C) 1997 Elsevier Science B.V.