Viscosity and Surface Tension of 1-Ethanol-3-methylimidazolium Tetrafluoroborate and 1-Methyl-3-octylimidazolium Tetrafluoroborate over a Wide Temperature Range

Room-temperature ionic liquids based on the imidazolium cation are presently widely studied, but more data on important properties such as viscosity and surface tension are required. In this work, two imidazolium-based ionic liquids, 1-ethanol-3-methylimidazolium tetrafluoroborate [C2OHMIM][BF4] and 1-methyl-3-octylimidazolium tetrafluoroborate [OMIM][BF4], were investigated. The former is a member of a new series that contains the alcohol (CH2)2OH as a functional group. The latter, already studied by several authors, has a long side chain in the imidazolium ring that is responsible for its surfactant properties. The surface tension was determined using the pendant drop technique in a wide temperature range, (298 to 470) K, which has never been explored before with ILs. The viscosity was measured using a new technique (a quartz crystal microbalance) between (288 and 328) K. The surface tension and the viscosity of [C2OHMIM][BF4] are unexpectedly high when compared with those of [OMIM][BF4]. The experimental values were interpreted in terms of the existing theories.