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The shirt you can't get dirty: Researchers create ultralight coating that can repel alcohol, coffee, oil and even petrol
Jul 15, 2017

Scientists have revealed the answer to every clumsy eaters worst nightmare - a coating that can be applied to clothing to make it repel almost anything you throw at it.

The unique coating, which is 95% air, can repel everything from coffee and alcohol to oil and even acid.

It is so light it can be used to create 'breathable' clothes to protect soldiers on the battlefield.

The nanoscale coating that's at least 95 percent air repels the broadest range of liquids of any material in its class, causing them to bounce off the treated surface, according to the University of Michigan engineering researchers who developed it.
In addition to super stain-resistant clothes, the coating 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 your shirt or your skin recoil when they touch the new 'superomniphobic surface'.

'Virtually any liquid you throw on it bounces right off without wetting it,' said Anish Tuteja, who led the study, which is published in the current issue of the Journal of the American Chemical Society.

'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,'

He and his colleagues tested more than 100 liquids and found only two that were able to penetrate the coating. 

They were chlorofluorocarbons—chemicals used in refrigerators and air conditioners. 

In Tuteja's lab, in a demonstration, the surface repelled coffee, soy sauce and vegetable oil, as well as toxic hydrochloric and sulfuric acids that could burn skin. 

Tuteja says it's also resistant to gasoline and various alcohols.

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,' or PDMS, and liquid-resisting nanoscale cubes developed by the 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 forces, known as 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 said. 

'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.

One classification of liquid that this coating repels is the so-called non-Newtonian category, which includes shampoos, custards, blood, paints, clays and printer inks, for example.

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