Roughness controlled superhydrophobicity on single nanometer length scale with metal nanoparticles

Abstract

Here we demonstrate high water pinning nanostructures and trapping of water droplets onto surfaces via control of roughness on a single nanometer length-scale generated by deposition of preformed gas phase distinct copper nanoparticles on hydrophilic and hydrophobic surfaces. It was found that the contact angles of the water droplets were increased to the superhydrophobic limit ∼150° at high nanoparticle coverages (≥80%) independent of the initial type of surface. The water droplets were trapped onto the surfaces by high adhesion forces similar like the rose petal effect. The droplets are in a Wenzel state at their outer part. Local nanocapillarity can force liquid into crevices between nanoparticles and push trapped air within the center of the droplet forming a Cassie–Baxter metastable state. Hence our approach to alter the wetting state is extremely straightforward without involving special micro/nano structuring facilities, but instead using direct single nanoparticles deposition on any type of surfaces creating a rough surface on a single nanometer length-scale, allowing due to its peculiar high water pinning and nanoporous structure liquid trapping phenomena.