A team of engineering researchers at the University of Michigan has developed a nanoscale coating that causes almost all liquids to bounce off surfaces treated with it. Creating a surface structure that is least 95 percent air, the new "superomniphobic" coating is claimed to repel the broadest range of liquids of any material in its class, opening up the possibility of super stain-resistant clothing, drag-reducing waterproof paints for ship hulls, breathable garments that provide protection from harmful chemicals, and touchscreens resistant to fingerprint smudges.
Made up of a mixture of rubbery plastic particles of “polydimethylsiloxane” (PDMS) and liquid-resisting nanoscale cubes containing carbon, fluorine, silicon and oxygen, the coating is applied to surfaces using a technique known as electrospinning, which uses an electric charge to create fine solid particles from a liquid solution. These solid particles that hug the pore structure of the surface it is applied to and create a finer web within those pores.
Similar to the way water droplets are suspended by air pockets created between tiny hairs on the surface of lotus leaves, the coating creates a structure that is 95 to 99 percent air pockets. This means that liquids coming into contact with the coating barely touch a solid surface, thereby reducing the intermolecular Van der Waals forces that normally draw two states of matter together.
"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," said Anish Tuteja, assistant professor of materials science and engineering, chemical engineering and macromolecular science and engineering. "We've drastically reduced the interaction between the surface and the droplet."
With so little surface are with which to interact, the droplets interact only with molecules of themselves. This means they stay intact, retaining a spherical shape and literally bounce off the treated surface.
So far, Tuteja and his colleagues have applied the coating to small tiles of screen and postage-stamp sized swatches of fabric. After testing more than 100 liquids, the researchers found only two that were able to penetrate the coating – both chlorofluorocarbons (CFCs) that are used as refrigerants in air conditioners and refrigerators.
Already proven effective on coffee, soy sauce, vegetable oil, gasoline, and various alcohols, the coating can also repel acids that could burn skin, such as hydrochloric and sulfuric acids. Tuteja says the coating is also the first demonstrated to repel low surface tension non-Newtonian liquids. These are liquids, such as shampoos, custards, blood, paints, clays and printer inks, that change their viscosity depending on the amount of force applied to them.
The team’s paper is published in the Journal of the American Chemical Society.
Tuteja demonstrates the nanoscale coating in the video below.
Source: University of Michigan
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