Thermocapillary instability of an ionic liquid-water mixture in a temperature gradient

Abstract

Ionic liquids have remarkable properties and are commonly harnessed for green chemistry, lubrication and energy applications. In this paper, we study a thermo-responsive Ionic Liquid (IL) solution which has the property of phase separating above a critical temperature, an interesting feature for the recovery of the IL-rich phase. For this purpose, we generate a temperature gradient in a microfluidic cavity where the confinement strengthens wetting effects and enhances the demixing. In this experimental configuration, we report the separation patterns along the phase diagram of the binary mixture composition. Three separation dynamics regime are identified that may display complex three-dimensional flows. In spite of this complexity, we rationalize all the observed regimes. Only two regimes lead to a complete spatial separation of the two phases. Interestingly, one is reminiscent of a Marangoni instability in radial geometry, even at confinement below 100 µm. We believe this work will find applications in the recycling of ionic liquids.

Waste heat recovery using thermally responsive ionic liquids through TiO2 nanopore and macroscopic membranes

“…We note that this could take advantage of our recent work emphasizing the influence of confinement on the phase separation of such IL-water mixtures. 50,51 Another prospective route could be the use of UCST (upper critical solution temperature) mixtures, with a phase separated system at room temperature and a recombination across a nanoporous membrane at higher temperature. The higher operating temperature of the diffusioosmotic module would lead to higher currents.…”