Roughness and topology of ultra-hydrophobic surfaces

Ultra-hydrophobic surfaces have considerable technological potential for various applications due to their extreme water repellent properties. When water contacts such surfaces, contact angles approaching 180degrees may be obtained. These surfaces owe their unique wetting properties to a subtle interplay between surface chemistry and mesoscopic topological structure. In this paper, we discuss the requirements regarding surface roughness for ultra-hydrophobicity. We demonstrate by numerical calculations of contact angles on idealized surfaces that the topological nature of the surface roughness has a major influence on the water repellency of hydrophobic surfaces. In order to validate this theory, we present an electrochemical method to experimentally determine important model parameters, characterizing the solid/liquid interface. Furthermore, we substantiate our theoretical findings with experimental data on contact angles on hydrophobic surfaces with well-characterized surface roughness and topology. (C) 2002 Elsevier Science B.V. All rights reserved.