A Functionalized High-Surface-Energy Ammonium-Based Ionic Liquid: Experimental Measurement of Viscosity, Density, and Surface Tension of (2-Hydroxyethyl)ammonium Formate

The ammonium-based ionic liquid (2-hydroxyethyl)ammonium formate has been known for ease of synthesis and great solvation properties. In this work, this ionic liquid was synthesized, and its temperature-dependent density, surface tension, and viscosity were measured. Surface tension was measured by the capillary rise method using a homemade capillary apparatus in which the liquid and vapor can be brought into equilibrium. Measurements of viscosity and surface tension were performed under a water-vapor-free atmosphere. The viscosity was measured using a capillary viscometer and found to fit the Vogel-Fulcher-Tammann (VFT) equation, indicative of a non-Arrhenius ionic liquid. Also, the viscosity of the ionic liquid was fitted quite accurately using the relation we developed recently with the characteristic exponent empty set = 0.166893. This ionic liquid has a rather high surface energy and low surface entropy, which can be attributed to the role of the -OH group involved. The determined surface thermodynamic properties could in part account for the good solvation properties shown by this ionic liquid.