Caffeine solubility in aqueous solutions of polyethylene glycol dimethyl ether 250: measurement and thermodynamic modeling

Abstract

ABSTRACT Molar solubility of caffeine in polyethylene glycol dimethyl ether 250 (PEGDME 250) + water mixtures over all mass fractions of PEGDME 250 were determined at 293.15–313.15 K under atmospheric pressure (≈ 85 kPa). The crystal forms of the caffeine in equilibrium with neat solvents of PEGDME 250 and water were analysed using X-ray powder diffraction and the results compared with the original caffeine. Also, the Hansen solubility parameters of caffeine and PEGDME 250 + water mixtures in the absence of caffeine were predicted. The studies of apparent thermodynamic analysis presented an endothermic and enthalpy-driven dissolution of caffeine. Moreover, the solubility of caffeine were correlated using various models; the van’t Hoff, mixture response surface, Jouyban–Acree, Jouyban–Acree–van’t Hoff, the modified version of Jouyban–Acree–van’t Hoff, the CNIBS/R-K, the Buchowski–Ksiazczak, the modified Wilson and modified Wilson–van’t Hoff models, acquiring average relative deviation values that were lower than 14.7%.