Phase Diagram of Ethylene Carbonate–Sulfolane System
О. Г. Резницких, Aigul S. Istomina, Sophia S. Borisevich, E. Yu. Evshchik, Е. А. Сангинов, О. В. Бушкова, Yu. A. Dobrovolsky
Abstract
Phase equilibria in the ethylene carbonate (EC)–sulfolane (SL) binary system were investigated using differential scanning calorimetry in a temperature range from –150 to +50°C to construct a phase diagram of the system. The EC–SL system belongs to a simple eutectic type, with a eutectic point of –16°C at 70 wt % of SL. It was noted that the EC-SL solutions have a tendency to supercooling in the composition range from 50 to 75 wt % of SL; the metastable liquid phase is characterized by a glass transition temperature Tg = –105°C. Reaching of an equilibrium state is hindered in the middle region of compositions; this can be explained in terms of strong dipole-dipole interactions between EC and SL molecules, whose intensity increases with decreasing temperature. Quantum-chemical calculations of the Gibbs energy of the formation of isolated dimers of various types, performed by the M052X method based on density-functional theory, confirm this assumption.