The Lotus effect involving roughness-induced superhydrophobicity is a way to design biomimetic non-wetting, non-sticky, self-cleaning, omniphobic, icephobic, and anti-fouling surfaces, which can be applied for various purposes related to green tribology. However, such surfaces require micropatterning, which is extremely vulnerable to even small wear rates. This limits the applicability of the Lotus effects to situations, when wear is practically non-present. To design sustainable superhydrophobic surfaces, we suggest using metal matrix composites (MMC) with hydrophobic reinforcement in the bulk of the material, rather than at its surface. Such surfaces provide roughness and heterogeneity needed for superhydrophobicity. In addition, they are sustainable since when surface layer is deteriorated and removed due to wear, hydrophobic reinforcement and roughness remains. We present a model and experimental data on wetting of MMCs. We also conduct experiments with graphite-reinforced MMCs and show that the contact angle can be determined from the model. In order to decouple the effects of reinforcement and roughness, the experiments were conducted for initially smooth and etched matrix and composite materials. Micropatterned surfaces can be used for underwater oleophobicity and self-cleaning, in a manner, similar to the Lotus effect. However, wetting of a rough surface by oil (or any non-polar organic liquid) can follow more complex scenarios than just wetting of a rough surface by water, since a four-phase solid–oil–water–air interface can be involved.
Contact Angle Water Droplet Water Contact Angle Graphite Particle Superhydrophobic Surface
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The authors acknowledge the support of the University of Wisconsin-Milwaukee (UWM) RGI, NSF I/UCRC for Water Equipment and Policy, and UWM Research Foundation Bradley Catalyst grants. The authors are also thankful to Prof. Pradip K. Rohatgi and Mr. Aniedi Nyong from the UWM Center for Composite materials for metallic samples.
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