Self-cleaning silicone gel insect wings

Researchers in Australia and the UK are flying the idea that insect wings could act as a model for making self-cleaning, frictionless, and superhydrophobic materials. They discuss the latest developments in their laboratories in a forthcoming issue of the International Journal of Nanomanufacturing.

Insects are incredible nanotechnologists. The surfaces of many insect wings have evolved properties materials scientists only dream of for their creations. For instance, some wings are superhydrophobic, due to a clever combination of natural chemistry and their detailed structure at the nanoscopic scale. This means that the wing cannot become wet, the tiniest droplet of water is instantly repelled. Likewise, other insect wing surfaces are almost frictionless, so that any tiny dust particles that might stick are sloughed away with minimal force.

Now, Gregory Watson of the James Cook University, in Townsville, Queensland, working with colleagues there and at Griffith University, and the universities of Queensland, and Oxford, are hoping to mimic these properties by using the surface of insect wings as a template for producing plastics, or polymeric, materials with novel surface properties.

If they are successful, they might then develop self-cleaning, water-resistant, and friction-free coatings for a wide range of machine components, construction materials, and other applications, including nano- and micro-electromechanical systems (NEMS and MEMS) and lab-on-a-chip devices for medical diagnostics and environmental sensing.

The team has carried out atomic force microscopy analysis of the surface of insect wings in order to determine the forces with which fine dust particles stick, or rather don't stick to the wing. That work confirms that only very small forces, just a few billionths of a Newton (2 to 20 nanonewtons) are needed to shed nanoscopic dust particles. 10 Newtons is the approximate force exerted by a 1 kg bag of sugar sitting on a kitchen work surface because of gravity. 2 nN is equivalent to the downward force of 100th imposed by a single grain of sugar.

'Many of the surfaces demonstrate superhydrophobic properties and will not only reduce the effects of contact with surfaces but also promote a self-cleaning function for removing foreign bodies,' the team explains.

With that data in hand, they then used wing membrane as a 'natural template' to cast a polymer surface and so duplicate the surface structure of the wing in PDMS, polydimethylsiloxane, the same type of silicone gel used in breast implants. One of the advantages of this approach is that no prior 'design' of the surface of the material is needed and so the team can exploit the enormous diversity of surface types from different insects and so produce materials with specific characteristics.