Preferential water condensation on superhydrophobic nano-cones array

Abstract

Condensed water droplet jumping on superhydrophobic surfaces has been a hot research topic during the last decade for various applications including enhancing condensation, antifogging, self-cleaning, electrostatic energy harvesting, and anti-icing/frosting surfaces. In the present work, a superhydrophobic nano-cone array is prepared by simple chemical bath reaction followed by silane modification. The tip of an individual nano-cone is only around 10 nm. The nano-cone array is also characterized by cavities among cones with varying sizes due to the imperfect alignment of individual nano-cones to the substrate. We demonstrate theoretically and experimentally that water condensation preferentially occurs within larger cavities among hydrophobized nano-cone arrays. After extrusion from cavities, droplets form a partial Cassie state which is a prerequisite of coalescence induced jumping. Moreover, growth rates of droplets extruded from larger cavities are larger than those from smaller cavities. Droplet jumping is observed at the very first coalescence and after multiple coalescence events under a microscope. The jumping droplet size is at tens of microns, demonstrating that droplets can be efficiently removed from the nano-cone array. In general, it is indicated that condensation can be controlled by purposely designing nano-scale structures, which would provide valuable suggestion for applications involving water condensation.