Nanoscale coating repels almost any liquid
A nanoscale coating that causes almost any liquid to bounce off surfaces treated with it has been developed by a team from the University of Michigan.
The superomniphobic coating is made up of a mixture of rubbery plastic particles of polydimethylsiloxane and liquid-resisting nanoscale cubes that contain carbon, fluorine, silicon and oxygen.
The researchers believe it could provide an advance towards stain-resistant clothing and waterproof paints that reduce drag on ships.
"Virtually any liquid you throw on it bounces right off without wetting it," commented lead researcher Anish Tuteja, an assistant professor of materials science and engineering. "For many of the other similar coatings, very low surface tension liquids such as oils, alcohols, organic acids, organic bases and solvents stick to them and they could start to diffuse through and that's not what you want."
To apply the coating, the researchers used a technique called electrospinning, which 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 material's chemistry means it hugs the pore structure of whatever surface it's being applied to, and also creates a finer web within those pores.
This structure means that between 95 and 99% of the coating is actually made up of air pockets, so any liquid that comes in contact with it 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.
"Normally, when the two materials get close, they imbue a small positive or negative charge on each other, and as soon as the liquid comes in contact with the solid surface it will start to spread," Tuteja explained. "We've drastically reduced the interaction between the surface and the droplet."
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.
