| The equilibrium solubility of naproxen (NAP) in the mixtures of polyethylene glycol dimethyl ether 250 (PEGDME 250) and water is determined at different temperatures (293.15–313.15 K). Some cosolvency models including the van’t Hoff, the mixture response surface (MRS), the Jouyban-Acree, the Jouyban-Acree–van’t Hoff, the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R-K), the Buchowski–Ksiazczak, the modified Wilson (MW) and the MW–van’t Hoff models can describe the equilibrium of solid–liquid systems successfully. Therefore, the performance of these models in correlation of current data was examined by calculation of average relative deviation (ARD%). The results present a good applicability of selected models in correlation of NAP solubilities; however, the van’t Hoff, CNIBS/R-K, MRS and Jouyban-Acree models (ARDs% ≤15.3) were more applicable than the others. At the end, the respective apparent thermodynamic quantities of dissolution and mixing processes, namely Gibb’s energy, enthalpy and entropy, are computed based on the van’t Hoff and Gibbs equations. |