Hydrophobic Metallic Nanorods coated with Teflon Nanopatches by Glancing Angle Deposition
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1188-LL09-03
Hydrophobic Metallic Nanorods coated with Teflon Nanopatches by Glancing Angle Deposition
Wisam J. Khudhayer, Rajesh Sharma, and Tansel Karabacak Department of Applied Science, University of Arkansas at Little Rock, AR, 72204 ABSTRACT Introducing a hydrophobic property to vertically aligned hydrophilic metallic nanorods was investigated experimentally and theoretically. First, platinum nanorod arrays were deposited on flat silicon substrates using a sputter Glancing Angle Deposition Technique (GLAD). Then a thin layer of Teflon (nanopatches) was partially deposited on the tips of platinum nanorod at a glancing angle of θ = 85o as well as at normal incidence (θ = 0o) for different deposition times. We show that GLAD technique is capable of depositing ultrathin isolated Teflon nanopatches on selective regions of nanorod arrays due to the shadowing effect during GLAD. Contact angle measurements on Pt/Teflon nano-composite have shown contact angle values as high as 138o, indicating a significant increase in the hydrophobicity of originally hydrophilic Pt nanostructures. Finally, a 2D simplified wetting model utilizing Cassie and Baxter theory of heterogeneous surfaces has been developed to explain the wetting behavior of Pt/Teflon nanocomposite.
INTRODUCTION Metallic nanostructures have attracted great attention due to their novel properties which are of high interest in many applications such as hydrogen production and storage, surface catalysis, and heat transfer, etc. [1]. Recently, the hydrophilicty of vertically aligned metal nanorods with sharp nanotips was investigated experimentally [1]. It was found that as the surface roughness increases, the contact angle of the metallic nanorods decreases and therefore these nanostructures resulted in hydrophilic surfaces. On the other hand, many studies have focused on utilizing Radio Frequency (RF) sputtering technique to deposit Polytetrafluoroethylene (PTFE), commonly known as Teflon, on rough surfaces to get superhydrophobic surfaces [2-8]. It has been documented that an increase in PTFE film surface roughness increases the contact angle of water and therefore hydrophobicity without altering the surface chemistry [2,3]. In these studies, the resulting Teflon coating was a continuous rough film that enhanced the hydrophobicity. However, as the micro- and nano-technology based systems emerge, conventional continuous PTFE coatings that completely cover the underlying surface may not be suitable for these applications as they block the desired transfer of photons/atoms/particles from/to the outside environment. Therefore, some applications may require “hydrophobic yet still isolated not-fully-coated nanostructured surfaces”. To the best of our knowledge, there is no reported
study on controlling the hydrophilicity of metallic nanorods with nanoscale roughness, even though there are many important applications for such nanostructures in surface catalysis, hydrogen production/storage, and heat transfer. In this work, a novel glancing angle deposition (GLAD)
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