"Superomniphobic" nanoscale coating repels almost any liquid

[frigidmagi]

gizmag

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.

There's a video at the link. Watch it.

[Josh]

That is so cool.

And this:

breathable garments that provide protection from harmful chemicals

I don't suit up and go in anymore, but I'm alllllll for that from both the perspective of somebody who's worn the gear as well as somebody who had to work with the extra safety concerns that PPE like that brings on, in terms of encumbrance and heat exhaustion/heatstroke risks.

[Batman]

While this sounds like a really interesting concept provided it can be made halfway affordable I'm not sure why they call it 'superomniphobic', which assuming I understand the term 'phobic' right would indicate a material that is seriously extremely afraid of everything, when what they're actually describing is a material that can, in fact, laugh at a lot of the threats it would be facing.

[Josh]

While this sounds like a really interesting concept provided it can be made halfway affordable I'm not sure why they call it 'superomniphobic', which assuming I understand the term 'phobic' right would indicate a material that is seriously extremely afraid of everything, when what they're actually describing is a material that can, in fact, laugh at a lot of the threats it would be facing.

You're assuming the material is rational enough to understand it shouldn't be afraid. Maybe it's kind of neurotic.

[Batman]

Okay, I have to admit that's an angle I didn't consider.

[Academia Nut]

On the one hand: cool. I've had projects based on this man's work.

On the other: dammit, stop pushing the field forward while I'm still working on this sort of thing!

Although with all of these sorts of things, there is something of a question of how durable these coatings actually are. PDMS is also known of as 'silicone rubber', which is to say that its not particularly strong, especially since the features are nanoscale projections and thus not particular good at resisting abrasion. Then again, things on the nanoscale can be surprisingly tough. There is also the question of how stable the drops are since with less than 5% solid contact there is the distinct possibility that mechanical vibration could cause the drops to collapse into a lower energy state.

Have to dig up the actual paper.

[Josh]

On the one hand: cool. I've had projects based on this man's work.

On the other: dammit, stop pushing the field forward while I'm still working on this sort of thing!

Although with all of these sorts of things, there is something of a question of how durable these coatings actually are. PDMS is also known of as 'silicone rubber', which is to say that its not particularly strong, especially since the features are nanoscale projections and thus not particular good at resisting abrasion. Then again, things on the nanoscale can be surprisingly tough. There is also the question of how stable the drops are since with less than 5% solid contact there is the distinct possibility that mechanical vibration could cause the drops to collapse into a lower energy state.

Have to dig up the actual paper.

Well in PPE terms you often don't expect your suit to be that durable. Your white tyvex is just plasticized paper, for example. The heavier class As are a bit more rugged, but the watchword for working the chemical environment is to always watch for anything that could compromise your gear. Sharp edges kill.

[Academia Nut]

When I saw "Not durable" I mean that leaning against a wall could destroy the protective properties, or forming a crease in clothing that has two surfaces rub against each other. The whole reason these things work is that you have sparsely dispersed nano-scale spikes or fibres of low surface energy material, and once the surface wears smooth it stops granting its superomniphobic properties. Depending on the exact material it is possible that part way through the wearing process it will become superomniphillic and draw in liquids.

[Josh]

When I saw "Not durable" I mean that leaning against a wall could destroy the protective properties, or forming a crease in clothing that has two surfaces rub against each other. The whole reason these things work is that you have sparsely dispersed nano-scale spikes or fibres of low surface energy material, and once the surface wears smooth it stops granting its superomniphobic properties. Depending on the exact material it is possible that part way through the wearing process it will become superomniphillic and draw in liquids.

Okay yeah that's very not good.

Thanks for the technical details and by all means keep up the good work.