Thermodynamic properties and phase transition studies of highly supersaturated solutions.

摘要

Thermodynamic and kinetic properties of highly supersaturated solution were investigated using the Electrodynamic Levitation Trap (ELT) with suspended a single charged microdroplet. This technique allows achievement at high supersaturation due to the absence of heterogeneous nucleation sites. Measurements of the water activity were made far into metastable zone and approaching the spinodal curve during the course of evaporation from the supersaturated droplet. By employing the Gibbs-Duhem equation, the solute activity of aqueous glycine solution was obtained as a function of concentration and temperature. Also, the nucleation induction time of highly supersaturated glycine solutions was measured and the nucleation induction time statistics were analyzed using two step nucleation model.;The polymorphic solid phase transformation for different polymorphs of glycine and theophylline are characterized using X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), and electrical conductivity measurements. The different polymorphs show different electrical impedance behaviors, which are ascribed to different crystalline phases identified by X-ray diffraction and differential scanning calorimetry. These studies indicate that the electrical impedance method is a useful and effective quantitative tool for determination of polymorphs in the solid state as compared to other characterization techniques.