Capturing airborne microparticles through the motions of liquid droplets.*

We present a novel liquid droplet-based microparticle filter inspired by the scavenging of dust particles by raindrops. Porous filters have been widely used to remove microparticles, but these filters are vulnerable to clogging with microparticles, leading to increased pressure loss and requiring frequent replacement. To overcome these limitations, the motions of liquid droplets are utilized to remove airborne microparticles. This method eliminates the clogging issue since the liquid droplet-based filter is free of solid porous structures. We found that the relative distance between the liquid droplet and the particle is a crucial factor. For small relative distances, microparticles are captured by liquid droplets, while for large relative distances, microparticles are deflected from their initial path by air currents induced by the motion of the liquid droplet, causing the microparticles to move far away from the droplets and thus leading to the failure of particle capture. These characteristics depend on the speed and shape of both the liquid droplets and particles. We visualize these interfacial dynamics using a high-speed camera and characterize their salient features by combining theory and experiments.