Phase separation of an ionic liquid mixture assisted by 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 thermoresponsive 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. We show that the phase separation is performed by the joint effects of sedimentation and thermocapillary actuation giving rise to a three-dimensional flow structure, which is quantitatively captured by our model. Altogether those mechanisms lead to the accumulation of the wetting phase near the heating source. We believe this work will find applications in the recycling of ionic liquids.