Viscosities of pure protic ionic liquids and their binary and ternary mixtures with water and ethanol

Abstract

The knowledge of the viscosity of ionic liquids is crucial for the design and development of industrial processes that involve these fluids, as well as for the theoretical study of this property. In this study, viscosities of four protic ionic liquids (PILs) consisting of ethanolamine as cation and formate, acetate, butyrate and hexanoate as anions, have been measured at the temperature range from 293.15 to 393.15 K, at atmospheric pressure. Viscosities of binary and ternary mixtures of these ionic liquids with water and ethanol at 293.15, 298.15 and 303.15 K have been also measured. PILs were found to be highly viscous fluids, except for 2-hydroxyethylammonium formate, and their viscosity is affected to a great extent by the presence of water and/or ethanol. The temperature dependency of the viscosity for pure ionic liquids is analyzed by means of the Vogel-Tammann-Fulcher equation, while for ionic liquid mixtures a modified Grunberg-Nissan equation is developed in this work. Satisfactory agreement between the experimental data and the model was obtained in all cases. Finally, the glass transition temperature of the PILs was measured.