J. Adhesion Sci. Technol., Vol. 21, No. 5–6, pp. 399–408 (2007)  VSP 2007. Also available online - www.brill.nl/jast Transparent ultra-hydrophobic surfaces P. F. RIOS 1,2 , H. DODIUK 1 , S. KENIG 1,∗ , S. McCARTHY 2 and A. DOTAN 1 1 Department of Plastics Engineering, Shenkar College of Engineering and Design, 12 Anna Frank St, Ramat-Gan 52526, Israel 2 Department of Plastics Engineering, University of Massachusetts at Lowell, 883 Broadway Street, Lowell, MA 01854-5130, USA Received in final form 29 January 2007 Abstract—Self-cleaning surfaces have received a great deal of attention, both in research studies and commercial applications. Both transparent and non-transparent self-cleaning surfaces are highly desired, as they offer many advantages and their potential applications are endless. As in many other cases, also in the case of self-cleaning surfaces, nature found a solution before man. The Lotus flower is a symbol of purity in Asian cultures, even when rising from muddy waters it stays clean and untouched by dirt, organisms and pollutants. The Lotus leaf “self-cleaning” surface is hydrophobic and rough, showing a two-layer morphology. While hydrophobicity produces a high contact angle, the two-layer morphology reduces the adhesion of dirt and water drops to the surface. Because of this low adhesion, water drops easily slide across the leaf surface carrying the dirt particles with them. In the present work the Lotus leaf morphology was mimicked using hydrophobic chemistry and a two- layer topography, with a base layer of silica and a top layer of intrinsically nanostructured polyhedral oligomeric silsesquioxanes (POSS) particles. Results have indicated that, thus, a transparent ultra- hydrophobic coating can be obtained. When these materials were mixed and used as a single layer the hydrophobicity deceased significantly. The contact angle and sliding angle measurements were supported by AFM micrographs. Keywords: Nanoroughness; Lotus effect; contact angle; sliding angle; hydrophobic surfaces; interfa- cial adhesion strength; coatings; POSS. 1. INTRODUCTION The thermodynamics between a liquid and a solid were first described by Young in 1805 [1]. The so-called Young’s equation relates the surface tensions of the liquid, the solid and the gas surrounding them to the contact angle formed between the liquid and the solid substrate. The contact angle is related to the generally used term “wetting”. Adamson [2] has defined wetting as a phenomenon where ∗ To whom correspondence should be addressed: Tel.: (972-3) 613-0111; Fax: (972-3) 613-0019; e-mail: samkenig@shenkar.ac.il