Self-sustaining levitation of droplets above a liquid pool

Abstract

In this Letter, we report the phenomenon of self-sustaining and long-term (>103 s) levitation of millimeter-sized droplets of a variety of liquids without any external forces. The droplet levitation is enabled by solutocapillary convection in the liquid pool, which occurs due to the surface tension gradient originating from non-uniform distribution of vapor molecules from the droplet at the pool surface. The droplet lifetime can be adjusted by adding the droplet liquid into the pool. The maximum levitation duration is achieved at a concentration that reduces the evaporation rate of the droplets and increases the solutocapillary flow in the pool. Such self-sustaining droplet levitation occurs under ambient conditions and can be used as an effective tool for studying the activity of viruses and microorganisms as they are transferred in airborne aerosols.