Production of small powder-stabilized droplets using superhydrophobic mesh

Abstract

Massive production of tiny droplets is critical for industrial processes and biomedical applications. Such droplets are formed by splitting the bulk liquid (top-down) or condensation to grow the droplet (bottom-up). Various generation methods have been reported; however, the generated droplets stick to the contacting substrate and/or coalesce into a larger droplet, limiting handling flexibility and/or size uniformity. Herein, tiny powder-stabilized droplets were massively generated by applying pulse pressure to a “powdered” superhydrophobic mesh on a water pool. The generated droplets were stabilized by a fine hydrophobic powder, namely, liquid marble, which does not coalesce or stick to the contact materials. The effects of mesh size, wettability, powdering, and applied pressure on the droplet formation dynamics were investigated. The generated droplet size depended on the mesh size and droplets were not formed on the hydrophilic mesh. When the superhydrophobic mesh gradually sank into the water pool to apply quasi-static hydro-pressure, the penetrated water did not split, and a continuous large water droplet was formed. However, tapping the superhydrophobic mesh to apply pulsed hydro-pressure induced multiple droplets to split through the mesh penetration. Without powder, the formed droplets coalesced to form large droplets. However, when the superhydrophobic mesh was powdered, the formed droplets were coated with the hydrophobic powder to form a liquid marble, preventing their coalescence.