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How To Make A Self-Cleaning Coating That Repels All Liquid

What is the best way to keep our screens clean? The first and obvious answer is that we keep our hands from dirt ourselves. But there's another possibility: self-cleaning coatings created by materials scientists.

Recently, Anish Tuteja, a materials researcher at the University of Michigan, developed a clear, smooth coating that repels all liquids and can be applied to any surface. (The research was published in the journal ACS Applied Materials & Interfaces .) Of course, there are other repellent coatings, but their capabilities are limited. Take, for example, a Teflon pan. "If you put a drop of water on it, it will get dirty, but if you give edible oil, it will spread," says Tuteja. "That happens on most surfaces." The material developed by his team is more versatile and hopes to be available in the coming years.

The Verge talked to Tuteja about the repellent as his team developed new materials and what's next for self-cleaning materials.

This interview has been easily edited for the sake of clarity.

You work on "surface science". What is surface science and what applications are there?

My group at the University of Michigan works mainly on different types of surfaces that attract or repel different liquids. It is a very unique surface that does not exist in nature but has many basic applications.

Regarding the defense against liquids, consider almost any surface around you and you can find an application of screen displays on tables and chairs and carpets. There is a lot of use for self-cleaning materials and dirt-repellent surfaces.

Another area is heat transfer to improve condensation on surfaces. This is relevant for all power plants and nuclear power plants in the world. [ Editor's note: Power plants generate steam that turns a turbine into electricity. The turbine is condensed to water and the process starts again, but the capacitors can be inefficient. ] It is also useful for cooling ̵

1; wherever there are phase changes or anything that goes from vapor to liquid would be relevant and helps save energy.

You said that these surfaces do not exist in nature, but what would be the closest naturally occurring material that has these properties?

Much of the work in the repellent area was on textured surfaces. These are rough surfaces that trap air bubbles in different liquids. The lotus leaf is the common example: water droplets come in and jump back.

That repels water, but not other materials like oil and alcohol. Take, for example, your non-stick Teflon pan. If you put a drop of water on it, it will get dirty, but if you give cooking oil, it will spread. That happens on most surfaces. There are no smooth surfaces that repel everything.

And your coating is a smooth surface that can repel liquids. You call it "omniphob". What does that mean exactly?

The surface resists wetting. Our definition of "omniphobic" coating means that liquid can not spread. Thus, various liquids such as water, oils and alcohol will not spread on the surface. In addition, the liquid droplets can slip off the surface very quickly, making them very easy to clean. So if you have a camera lens with the coating, you can tilt the surface and any water or oil on it will just slip off.

I was interested in how you came up with the idea. Instead of mixing materials, many calculations had to be done to see what could work together, right?

Absolutely. To make a repellent, usually take a material called filler and a polymer binder and mix them together. The polymer binder provides durability and the filler provides these repellency. One might think that by taking the most durable filler and the most durable polymer and mixing them together, you get the most durable surface.

That's not the case. What's really important is how well these components mix and interact, what we call "miscibility". Instead of mixing and matching, we have performed our own calculations of the properties of many substances to find the best area. We've developed mathematical formulas that could fit together well, and that means we're not limited to a single formulation. It allows us to look at different polymers and different fillers and find out which probably have similar properties. This will allow us to predict what the best substances might be.

How does the coating feel? And how long would it take? Suppose I use the coating on my iPhone – when do I have to reuse it?

It's pretty thin and it's hard. It's based on urethane, a rubbery material that feels like a stiff rubber coating. How long it would take depends on the exact formulation, but we hope for something on the order of a year.

How about putting these on the market? When will that happen?

We are actively working to bring such surfaces to the market. We are working with a co-founded startup Hygratek to bring it to market within the next one to two years.

The biggest challenge we want to face is the durability of the coating and how it feels good. And of course you want to make sure that the costs are not too high. We try to find an optimal formulation, not just one, to see which would be the least expensive.

Do we really know that this has no health effects?

We test. The molecule in this paper contains fluorine, and there's a lot of data we have about how it's not toxic. But there are things in progress that we need to find out. And this particular molecule is still available in relatively small quantities, which is why we are looking for other formulations that are non-toxic and based on commercially available materials, other combinations of polymers.

What are you still working on? What else is being developed in the field of surface science?

We also work on omniphobic coatings that repel or kill microbes, as well as materials that are icephobic. In these, ice is not liable, so it would be very useful for aircraft runways and power lines and wind turbines. We also make dustproof surfaces.

In the area of ​​surfaces attracting water, we create surfaces that attract water but repel oil. Nothing like this exists in nature, where you can get oil to the beads, but water that spreads to the surface. These membranes could be used, for example, to remove oil spills.

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