Permeation by Electrowetting Actuation: Revealing the Prospect of a Micro-valve Based on Ionic Liquid

The electrowetting behavior of ionic liquid significantly promotes microfluidic technology due to the advantage of manipulation of ionic liquid without additional mechanical parts. Recently, a novel micro-valve that shows good prospects was proposed by MacArthur et al. based on the permeation of ionic liquid under electric field. Inspired by their work, the permeation process of ionic liquid (EMIM-Im) droplets actuated by electrowetting was investigated in this work using molecular dynamics simu-lation. The wettability of substrate, electric field strength and electric field polarity were varied to inves-tigate their influences. On the substrate side, results showed that the hydrophilic substrates tend to stretch and adsorb the droplet and hence hinder the permeation process, whereas the hydrophobic sub-strates facilitate permeation due to their low attraction for liquid. Particularly, super hydrophilic sub-strates should be avoided in practice, because their strong adsorption effects will override the electric field effects and disable the permeation process. On the electric field side, results showed that increased electric field strength enhances the permeation, but varying electric field polarity will result in an asym-metric permeation behavior, which was found to be the result of the different evaporation rate of the ion species that ultimately caused a non-charge-neutral droplet. Our investigation then uncovered the two critical roles of the electric field: elongating the droplet and providing the driving force for the permeation. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study investigated the permeation process of ionic liquid droplets actuated by electrowetting using molecular dynamics simulation. The results showed that the wettability of the substrate and the electric field strength have significant influences on the permeation process, while varying electric field polarity results in asymmetric permeation behavior. The study also revealed the critical roles of the electric field in elongating the droplet and providing the driving force for permeation.