Nanotech Coating Provides Liquid-Repellent Surface

Liquid repellent coating (Joseph Xu, University of Michigan)

Materials scientists at University of Michigan in Ann Arbor and Air Force Research Lab at Edwards Air Force Base in California developed a new coating material that can repel virtually any liquid from a surface. The team led by Michigan engineering professor Anish Tuteja reported its findings in the current issue of the Journal of the American Chemical Society (paid subscription required).

The coating is made of rubbery plastic particles of polydimethylsiloxane, a polymeric organic silicon compound, combined with liquid-resisting nanoscale cubes — 1 nanometer equals 1 billionth of a meter — developed by the Air Force that contain carbon, fluorine, silicon and oxygen. As important as the chemistry is the texture of material, which in this case binds to the pore structure of the surface where it’s being applied. That texture also creates a finer web within those pores.

Tuteja’s team applied the material using a technique called electrospinning that creates with an electric charge fine particles of solid from a liquid solution. With this process, the researchers coated small tiles of screen and postage-stamp-sized swaths of fabric.

The structure of the coating means that nearly all — from 95 and 99 percent — of the coating is actually air pockets, thus liquids that come in contact with the coating are largely kept from touching a solid surface. Because of this super-light touch, the liquid touches only filaments of the solid surface.

As a result, the coating reduces to a minimum the intermolecular forces that normally draw the two states of matter together. With little molecular force encouraging the liquid to spread, the droplets stay intact, staying in a spherical shape, and literally bouncing off the coating.

The researchers tested more than 100 liquids on the coated samples and found the coating repelled coffee, soy sauce, and vegetable oil, as well as toxic hydrochloric and sulfuric acids that could burn skin. Tuteja says the coating also resists gasoline and various alcohols. Only two fluids were able to penetrate the coating, both of which were chlorofluorocarbons, the chemicals used in refrigerators and air conditioners.

“Virtually any liquid you throw on it bounces right off without wetting it,” notes Tuteja. “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.”

The liquid-repellent coating has a wide range of potential applications. Super stain-resistant clothes could extend the life and reduce maintenance for clothing. In addition, the coating could be used to produce breathable protective garments from chemicals for soldiers and scientists, and advanced waterproof paints that reduce the drag of water on ships.

In the following video, Tuteja and colleagues demonstrate the coating.

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