Nature’s Raincoats was part of the Royal Society Summer Science Exhibition 2009 that took place from Tuesday 30th June 2009 to Saturday 4th July 2009 at The Royal Society in London. The exhibit was one of 21 selected from 103 proposals on the basis of scientific quality and novelty, and attractiveness in promoting science to the general public, post-16 students, policy makers, and the press. The exhibit was based on research at Nottingham Trent University and the University of Oxford on bio-inspired super water-repellent surfaces, and was presented as a collaborative public understanding of science exhibition.
The exhibit provided a glimpse into the natural world of super water repellency, a feel for the droplet shedding and self-cleaning capability of smart surfaces, an understanding of the sound of pressure and a peek at future technological possibilities.
Heading image courtesy Gary Early.
A hands-on, interactive exhibit, the stand was divided into several zones. The sections below give a flavour of the activities, technologies and applications showcased in the exhibition.
Superhydrophobic plant ‘forest’ & wet area
This area of the exhibit contained a range of superhydrophic plants. You can read about many of them in the Bioinspiration – Plants section of this website.
Activities included drip spheres and magic sand:
Hydrophobic sand immersed in water retains a layer of air around itself and comes out dry. Sand underwater can be seen to glisten with a silvery sheen due to the layer of air it retains. The sand can be sculpted underwater and when spooned out, comes out dry
Now a common children’s toy, magic sand is said to have first been developed to clean up ocean oil spills and then as the bedding material for laying pipes in areas that have severe winters and frozen ground.
Animal bioinspiration & technology
Super liquid-repellent and self-cleaning surfaces have many potential applications. These include the dirt repelling StoCoat™ Lotusan® exterior building paint, hydrophobic concrete designed to reduce rusting of the reinforcing bars, self-cleaning clothes that resist wine stains, water-repellant swimwear, mPhase Technologies long lasting reserve batteries, Gore-Tex® fabric in breathable clothing, solar panel and radar dome coatings to prevent build-up of scattering droplets, as lens coatings in high tech optics (e.g. Zeiss LotuTec®) or even as the basis for the Harry Potter Water Maze game. Many more potential applications are under development by companies across the world.
Pushing against many points spreads the force and reduces pressure. In this demonstration a balloon pushed hard against a bed of nails doesn’t pop, but when pushed gently against a single nail, the nail penetrates the skin of the balloon and it pops easily.
On a superhydrophobic surface there are many hydrophobic features on the surface (the ‘nails’) and these are unable to penetrate the ‘skin’ of a water droplet caused by surface tension.
Living and breathing underwater doesn’t always need gills. The water (or diving bell) spider has a plastron on its back, which it uses to transport air into a silken nest that it builds underwater. The diving bell itself acts as a sophisticated aqualung.
Muddying a superhydrophobic surface is far from easy. In this demonstration of the Lotus-Effect®, a superhydrophobic surface is plunged into a mud box and comes out clean. StoCoat™ Lotusan® is an exterior building paint that uses the self-cleaning and non-stick properties of superhydrophobic surfaces.
Super-vortex: skating across surfaces
A popular charity collection box is a coin vortex funnel – coins go round and round before dropping through the hole. When a jet of water is used on an ordinary funnel it quickly goes down the plug, as shown in video 1. In video 2, a jet of water is shown on a funnel with a superhydrophobic surface. The jet breaks up into droplets and goes round many more times than on an ordinary surface.
Bioinspiration – Animals
We ran a photographic competition for the Royal Society Summer Science Exhibition to find who could take the best, most imaginative photograph showing the interaction of water with natural or man-made surfaces. The competition is now closed! Many thanks for all the interesting photographs submitted. The entries were judged by award winning photographer James Stenson.