Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion

Bharat Bhushan

Bharat Bhushan

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics, Ohio State University201 West 19th Avenue, Columbus, OH 43210, USA

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Yong Chae Jung

Yong Chae Jung

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics, Ohio State University201 West 19th Avenue, Columbus, OH 43210, USA

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Kerstin Koch

Kerstin Koch

Nees Institute for Biodiversity of Plants, Rheinische Friedrich-Wilhelms University of BonnMeckenheimer Allee 170, 53115 Bonn, Germany

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    Superhydrophobic surfaces exhibit extreme water-repellent properties. These surfaces with high contact angle and low contact angle hysteresis also exhibit a self-cleaning effect and low drag for fluid flow. Certain plant leaves, such as lotus leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical roughness of their leaf surfaces. The self-cleaning phenomenon is widely known as the ‘lotus effect’. Superhydrophobic and self-cleaning surfaces can be produced by using roughness combined with hydrophobic coatings. In this paper, the effect of micro- and nanopatterned polymers on hydrophobicity is reviewed. Silicon surfaces patterned with pillars and deposited with a hydrophobic coating were studied to demonstrate how the effects of pitch value, droplet size and impact velocity influence the transition from a composite state to a wetted state. In order to fabricate hierarchical structures, a low-cost and flexible technique that involves replication of microstructures and self-assembly of hydrophobic waxes is described. The influence of micro-, nano- and hierarchical structures on superhydrophobicity is discussed by the investigation of static contact angle, contact angle hysteresis, droplet evaporation and propensity for air pocket formation. In addition, their influence on adhesive force as well as efficiency of self-cleaning is discussed.

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