Interfacial tension and wetting properties of 1-ethyl-3-methylimidazolium tetrafluoroborate in carbon dioxide, from atmospheric pressure to supercritical state

Abstract

In this study, the interfacial tension and wetting properties of [Emim][BF4] (1-ethyl-3-methylimidazolium tetrafluoroborate) in CO2 were measured at pressures from 0.1 to 15.0MPa and temperatures between 308.15 and 343.15K. Economical modifications of the commercial interfacial apparatus were implemented to pre-saturate the [Emim][BF4] phase by CO2 for the measurement of interfacial tension and production of small sessile droplets for contact angle measurements. The interfacial tension was found to be mainly dependent on CO2 solubility in the [Emim][BF4] phase, and a linear fitting equation was proposed. The contact angles of the [Emim][BF4] phase on quartz, 316L stainless steel, and polytetrafluoroethylene (PTFE) in CO2 atmosphere were analyzed to predict the interfacial tension differences between CO2/solid and IL/solid phases. The reduction of interfacial tension difference was caused by increased CO2 solubility in the [Emim][BF4] phase at low pressure for quartz and 316L stainless steel dense solids. The polymer PTFE material behaved very differently, being susceptible to swelling in compressed CO2.