Polythermal studies of the water – propylene glycol systems by densitometry, viscometry and spin probes method

Based on the determined values of density, dynamic viscosity and molar volumes, the thermodynamic activation parameters and excess thermodynamic activation parameters of viscous flow at temperatures from 293.15 K (20°C) to 313.15 K (40°C) were calculated for the mixed binary solvents water – propylene glycol (PG). Using the isotherms at 298.15 K, assumptions were made about the composition regions of binary solvents with different structural organizations. The structure of the mixed solvent has an impact on the various functional characteristics of the systems water – PG, and it could also influence the performance of medicinal products with a liquid dispersion medium. The density and excess density, as well as the dynamic viscosity and excess dynamic viscosity for systems water – PG were determined as a function of the PG concentration. Using the method of spin probes, it was demonstrated that changes in the dynamic viscosity of systems water – PG correlated with the alterations in the viscosity of the microenvironment of spin probe molecules. The viscosity of the microenvironment was also influenced by the interaction between molecules of dissolved spin probes and solvent molecules.