Delivered by Publishing Technology to: Kyung Hee University IP: 163.180.121.209 On: Tue, 19 Mar 2013 01:34:28 Copyright American Scientific Publishers RESEARCH ARTICLE Copyright © 2013 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 13, 1884–1887, 2013 Low Cost Fabrication of a Superhydrophobic V -Grooved Polymer Surface Steven M. Hurst 1 , Bahador Farshchian 1 , Lance Brumfield 1 , Jeong Tae Ok 1 , Junseo Choi 1 , Jinsoo Kim 2 ∗ , and Sunggook Park 1 ∗ 1 Mechanical Engineering Department and Center for Bio-Modular Multiscale Systems Louisiana State University, Baton Rouge, LA 70803, USA 2 Department of Chemical Engineering, Kyung Hee University, Yongin 446-701, Korea Engineering of polymer surfaces to control their wetting properties has shown a wide range of potential applications. In this paper we show low cost fabrication of a superhydrophobic polymer surface via a hierarchical combination of hot embossing, O 2 reactive ion etching (RIE) and depo- sition of a hydrophobic silane. The hot embossing and O 2 RIE were used to produce respective micro and nanoscale surface roughness which is a requirement for obtaining superhydrophobic sur- faces, while the deposition of a hydrophobic silane modified surface chemistry. In order to increase the water/air interface in the Cassie-Baxter composite wetting model, a brass mold with microscale V -grooves was used for hot embossing. Images of droplets in both static water contact angles and dynamic impact tests with the surface clearly show that the wetting state follows the Cassie-Baxter wetting model. The results of this study indicate that our design of the dual level surface roughness and the fabrication process allow for low cost and easy production of a highly superhydrophobic surface. Keywords: Superhydrophobic Surfaces, Hot Embossing, Reactive Ion Etching, Silane Deposition. 1. INTRODUCTION The design of micro and nanoscale structures and chemistry for superhydrophobic surfaces has given rise to a broad range of applications which ranges from drag reduction 1 and improved mixing in microfluidic devices, 2 to self- cleaning 3 4 and anti-oxidative surfaces. 5 Hierarchical or dual scale micro and nanostructures (or roughness) together with chemical modification are believed to enhance the surface hydrophobicity, leading to a focus on the development of low cost fabrication methods for 3-D or combined micro and nanoscale structures. Water contact angles on a rough surface are usually described by either Wenzel 6 and Cassie-Baxter 7 models. In the Wenzel model, the liquid is in intimate contact everywhere with the rough surface while the Cassie-Baxter model introduces the idea of a partially supportive air pocket between the roughened surface and the liquid. In the Cassie-Baxter wetting state, the liquid droplet may only contact a small fraction of the rough surface, leading to very low friction between the surface and droplet, and consequently a low sliding angle. For this reason, a true ∗ Authors to whom correspondence should be addressed. superhydrophobic surface requires the Cassie-Baxter wet- ting state. Fabrication of superhydrophobic surfaces in polymers has drawn significant interests due to low cost fabrication modalities, such as hot embossing and injection molding, as well as the versatility in the selection of an appropriate material due to the availability of a wide range of dif- ferent polymers. In one approach, nanoporous anodized alumina is used as a stamp for polymer molding to pro- duce nanoscale surface roughness, which was combined with various methods to add microscale roughness to the surface such as micromachining using a tungsten car- bide needle, 8 micro-indentation, 9 and imprinting with a hydraulic press. 10 However, water contact angles measured on those polymer surfaces even with hierarchical micro and nanoscale surface structures are reported to be around 140  , much lower than those reported on silicon-based substrates with similar surface roughness. Jeong et al. recently showed that water contact angle increases as the spacing-to-width ratio for microstructures of the hierarchi- cal micro and nanostructures increases, in agreement with the Cassie-Baxter wetting model. They also demonstrated superhydrophobic structures in polyurethane acrylate with contact angles larger than 160  . 11 Therefore, the literature 1884 J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 3 1533-4880/2013/13/1884/004 doi:10.1166/jnn.2013.6973