Effect of surface treatment on wetting behavior of copper

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Abstract

Super-hydrophobic surfaces are very useful in cleaning activities. Surfaces with water contact angles above 150° are regarded as superhydrophobic surfaces. In the present study an attempt has been made to achieve superhydrophobicity on copper substrate by electrochemical etching and electro–deposition of Co–Ni alloy and Co–Ni-Graphene composite. A contact angle of about 105° was obtained on Cu surface with electro-deposited Co–Ni alloy and on electro-deposited Co–Ni–G alloy contact angle was found to be 106°. The contact angle was significantly higher at about 142° with electro etched surface. Corrosion test was carried out with electrochemically etched Cu. Electrochemical etching time was varied from 30 to 240 min. The electro-etched Cu substrate etched for 60 min. showed better corrosion resistance with a corrosion rate of 0.197 mm/year. The surface topography of both etched and electrodeposited samples was studied by atomic force microscopy (AFM) and the results were correlated with the wettability data.

Introduction

Wetting is one of the most important properties of liquids to spread over a solid substrate. Wetting of a solid by liquid is of great technological importance. Some applications require a good wetting between liquid and substrate surface such as soldering and printing whereas some others demand poor wetting (repellence) such as painted surface and solar panels. Contact angle is a measure of the degree of wetting or wettability of a surface by a liquid [1].

Wettability is an important characteristic of solid surfaces, and is usually measured by the contact angle between water and the surface. If the contact angle is less than 90°, the surface is hydrophilic; if it is greater than 90°, the surface is hydrophobic and if it is greater than 150°, the surface is superhydrophobic [2]. A super-hydrophobic surface is the one that repels water to such an extent that contact angles obtained are extremely high; they are generally defined as surfaces with water contact angles above 150° but it has also been less commonly adopted as 140° [3]. The microscopic geometric structure of the surface is one parameter which determines wettability; Free energy is another parameter- higher the free energy, higher is the wettability, and vice-versa. In general, a solid surface becomes hydrophobic when treated to give micro- or nano-roughness structures and low surface energy. Many kinds of surface treatment techniques, including optical micro-lithography, dry and wet etching, surface coating and precision diamond dicing processes were reported [4], [5], [6], [7]. To reduce the production costs and increase the processing speeds, laser machining processes techniques such as laser ablation, laser milling, and laser deposition have been employed [8], [9], [10]. These techniques have been effectively used to manufacture components with enhanced hydrophobic properties.

There is little research is carried out on the developing a simple technique of fabricating super-hydrophobic surfaces on various substrates. Realization of super-hydrophobic surfaces via simple coating methods to design a solid surface with appropriate surface roughness and low surface energy are rarely attempted [11].

Different topography can be achieved by creating rough surface either by etching or by coating the surface. Wenzel regime indicates the roughness and Cassie-Baxter model indicates the low surface energy materials in superhydrophobic surfaces. Nano-particles, especially silica nanoparticles are used to create appropriate roughness on a surface [12], [13].

Silica nanoparticles can create hierarchical structure with nano or microscale roughness on a substrate surface. Many polymers are hydrophobic in nature and fluorocarbons such as Teflon exhibit low surface energy, however these materials are thermally stable and can be used in water proof clothing, concrete and paint with very low friction [14], [15]. In the present study, an attempt has been made to fabricate a hierarchical superhydrophobic surface including micro and nanostructure from graphene nano particles by elecro-chemical coating and electrochemical etching on copper subatrate.

Section snippets

Materials and methodology

A 99% pure copper sheet was used as metallic substrate (20 mm × 70 mm, 1 mm thick) on which coating and etching were done. To achieve mirror finish on copper surface 400, 1200 and 2000 grade emery papers were used. Final polish was carried on a disc polisher. The coating was done with graphene nano particles in solution with Copper–Nickel. Pure Nickel plate was taken as an electrode. The electrochemical etching and deposition was performed. Trichloroethylene (CHCl.CCl2) was used to clean the Cu

Results and discussion

The surface topography observed by AFM are shown in Fig. 1. For electroetched Cu surfaces and Co-Ni alloy deposited Cu and Co–Ni–graphene deposited Cu surfaces. The average roughness of bare copper was found to be 20.6 nm. The copper surfaces electroetched for 60 min and 240 min had average roughness of 203 nm and 243 nm respectively which shows that the treated surfaces were rougher. The average roughness was found to be 145 nm for Co–Ni alloy deposited Cu surface at current density of

Conclusion

A near superhyphobic surface has been achieved on etched copper substrate with a contact angle of 142.1°. For the same electroetching time, the substrate showed better corrosion resistance with a corrosion rate of 0.197 mm/year which was lower compared to other etched samples. Electro-deposition of copper substrate with Co–Ni alloy and Co–Ni–Graphene composite made the surface to be hydrophobic but not superhydrophobic. Better hydrophobicity or Poor wettability was achieved for an optimum

Acknowledgement

Mr. Koushik N, Mr. Jameson Keisham, Mr. Avinash Poojary and Mr. Lathesh, Final year undergraduate students of Department of Mechanical Engineering, Alva’s Institute of Engineering & Technology for helping us to conduct experiments.

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