Bioinspired Directional Surfaces

An engineered anisotropic nanofilm with unidirectional wetting properties. Anisotropic textured surfaces allow water striders to walk on water, butterflies to shed water from their wings and plants to trap insects and pollen. Capturing these natural features in biomimetic surfaces is an active area of research. Here,we report an engineered nanofilm, composed of an array of poly(-xylylene) nanorods, which demonstrates anisotropic wetting behaviour by means of a pin-release droplet ratchet mechanism. Droplet retention forces in the pin and release directions differ by up to 80 uN, which is over ten times greater than the values reported for other engineered anisotropic surfaces. The nanofilm provides a microscale smooth surface on which to transport microlitre droplets, and is also relatively easy to synthesize by a bottom-up vapour-phase technique. An accompanying comprehensive model successfully describes the film’s anisotropic wetting behaviour as a function of measurable film morphology parameters.

Hancock MJ, Sekeroglu K, Demirel MC. Bioinspired directional surfaces for adhesion, wetting, and transport. Advanced Functional Materials, 2012, 22 : 2223–2234. [pdf]

Malvadkar NA†, Hancock MJ†, Sekeroglu K, Dressick WJ and Demirel MC. An engineered anisotropic nanofilm with unidirectional wetting properties. Nature Materials, 2010, 9 : 1023–1028 [pdf]