1 - Most liquids won't wet this material

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Most liquids won't wet this material

17 January 2013

A nanoscale coating that's at least 95 percent air is able to repel the broadest range of liquids of any material in its class, causing them to bounce off the treated surface.

An uncoated tile of screen is wetted by liquids (left), but a treated piece remains dry. Photo: Joseph Xu, University of Michigan Engineering Communications

In addition to super stain-resistant clothes, the coating - developed by a team of engineering researchers at the University of Michigan - could lead to breathable garments to protect soldiers and scientists from chemicals, and advanced waterproof paints that dramatically reduce drag on ships.

Droplets of solutions that would normally damage either garments or skin simply recoil when they touch this new 'superomniphobic surface'.

To apply the coating, the researchers use a technique called electrospinning that uses an electric charge to create fine particles of solid from a liquid solution. So far, they've coated small tiles of screen and postage-stamp-sized swaths of fabric.

The coating is a mixture of rubbery plastic particles of polydimethylsiloxane (PDMS), and liquid-resisting nanoscale cubes developed by the US Air Force that contain carbon, fluorine, silicon and oxygen. The material's chemistry is important, but so is its texture. It hugs the pore structure of whatever surface it's being applied to, and it also creates a finer web within those pores.

This structure means that between 95 and 99 percent of the coating is actually air pockets, so any liquid that comes in contact with the coating is barely touching a solid surface. Because the liquid touches mere filaments of the solid surface, as opposed to a greater area, the developed coating can dramatically reduce the intermolecular forces that normally draw the two states of matter together. These Van der Waals interaction forces are kept at a minimum.

With almost no incentive to spread, the droplets stay intact, interacting only with molecules of themselves, maintaining a spherical shape, and literally bouncing off the coating.

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