Conversion of a Metastable Superhydrophobic Surface to an Ultraphoblic Surface.pdf

Conversion of a Metastable Superhydrophobic Surface to an Ultraphobic Surface Xue-Mei Li,* ,?,? Tao He, ?Mercedes Crego-Calama, ?and David N. Reinhoudt* ,? State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Uni Versity of Technology, 5 Xinmofan Road, China, 21009, and Laboratory of Supramolecular Chemistry and Technology Group, MESA +Institute for Nanotechnology, Uni Versity of Twente, . Box 217, 7500AE Enschede, herlands Recei Ved April 3, 2008. Re Vised Manuscript Recei Ved May 13, 2008 Superhydrophobic surfaces in Wenzel and metastable wetting state were prepared and the conversion of such surfaces to ultraphobic surfaces was reported by the application of a ?ne-scale roughness. Silicon nitride substrates with hexagonally arranged pillars were prepared by micromachining. The two-scale roughness was achieved by coating these substrates with 60 nm silica nanoparticles. The surface was made hydrophobic by silanization with octadecytrichlorosilane (OTS). Wettability studies of the silicon nitride ?at surface, silicon nitride pillars, and the surfaces with two-scale roughness showed that a two-scale roughness can effectively improve the hydrophobicity of surfaces with a higher apparent contact angle and reduced contact angle hysteresis when the original rough surface was in a metastable or Wenzel state. This