# Difference between revisions of "Superhydrophobic surfaces"

Started by Lauren Hartle, Fall 2011.

Entry has been combined with Superhydrophobicity, Superhydrophicity (misspelled) and Superhydrophobic. (LH 2011)

## Introduction

A water droplet on a superhydrophobic surface has a contact angle of greater than 150 degrees and a very low roll-off angle. In nature and in man-made materials, this has been achieved with Structured Surfaces. Advantages of such surfaces include the ability to repel water and self-clean.[3] Industrial applications include "self-cleaning window glasses, paints, and textiles to low-friction surfaces for fluid flow and energy conservation."[2] To understand why water droplets wet these surfaces so poorly, one m

Figure from reference 1.

Wenzel: $\cos{\theta}_c = r \cos{\theta}$

where r is the ratio of the actual area to the projected contact area. Cassie-Baxter: $\cos{\theta}_{c} = \phi \left( cos \theta + 1 \right) - 1$ $cos \theta < \frac {\phi - 1}{r -\phi}$

It is argued that surface structure can produce superhydrophobic effects, even on a hydrophilic surface. For example, lotus leaves have been shown to be superhydrophobic, despite the waxy, weakly hydrophilic coating on the surface.[1] It has been demonstrated that the surface of a lotus leaf is superhydrophobic in part due to the presence of hierarchical surface structures structures consisting of micro- and nano-scale features. [2] Butterfly wings and parts of pitcher plants have observed superhydrophobic properties.

Figure from reference 2.

## References

[1]"Design parameters for superhydrophobicity and superoleophobicity". Anish Tuteja, Wonjae Choi, Gareth H. McKinley, Robert E. Cohen, and Michael F. Rubner. MRS Bulletin 33 (8), 752-758 (August 2008)

[2]"Fabrication of artificial Lotus leaves and significance of hierarchical structure for superhydrophobicity and low adhesion". Kerstin Koch, Bharat Bhushan, Yong Chae Jung and Wilhelm Barthlott. Soft Matter, 2009, 5, 1386–1393.

[3]"Self-cleaning materials: Lotus leaf inspired nanotechnology" Peter Forbes, Scientific American 30 July 2008.