Harnessing Reversible Wetting Transition to Sweep Contaminated Superhydrophobic Surfaces.

Sweeping deposited particles is absolutely essential in order to maintain the excellent functionality of superhydrophobic surfaces. Many methods have been proposed to sweep microparticles deposited on tips of micro/nanostructures. However, how to sweep nanoparticles trapped in cavities of superhydrophobic surfaces has remained an outstanding issue. Here, we show that harnessing the reversible wetting transition provides a feasible way to sweep such nanoparticles. Using molecular dynamics simulations, we demonstrate that the electrically induced CB-W wetting transition makes liquid intrude into a groove and wet a trapped hydrophilic nanoparticle; however, once the electric field is removed, a spontaneous W-CB dewetting transition happens, and the extruded liquid transports the hydrophilic nanoparticle to the groove top, successfully picking up the trapped hydrophilic nanoparticle. We further find that the adhesion between the nanoparticle and groove bottom wall hinders the successful pickup, and picking up such a nanoparticle requires a stronger particle hydrophilicity. With the introduction of amphiphilic Janus particles into a liquid, we exhibit that the electrically induced reversible wetting transition can also successfully pick up a trapped hydrophobic nanoparticle. By means of calculations of the potential of mean force (PMF), we reveal pathways of both the CB-W wetting transition and the W-CB dewetting transition and hence answer why and how a hydrophilic or a hydrophobic nanoparticle is picked up successfully.