permanent superhydrophobic coating on metal?

[ivymike]

Hello all,

After reading about this:

http://www.nature.com/nature/journal/v489/n7415/extref/nature11418-s1.pdf

I have a practical application in mind, and would like to see whether there are permanent superhydrophobic coatings that would be suitable for application to steel and/or iron surfaces. Anyone have any hints on that? I've sent an email to the company behind NeverWet, and also to the Soft99 people.

The NeverWet product looks very interesting...but I got worried while watching the video about coating an electronic board when he mentioned that the coatings last for "hours" under a shower... uh, sorry, I was hoping for 20,000 hours!

 

[zdas04]

I sat in a meeting in 1980 where some research scientists were presenting the conclusion of 10 years of work on changing the wetability of a rock from oil-wet to water-wet. Their conclusion at the time was that there were no commercially available products able to change the wetabiliity of a rough surface (they talked about the products that were emerging for car mirrors as needing a very smooth surface). From that presentation it was clear that if you could change a rock from oil-wet to water-wet it would be worth trillions of dollars to the Oil & Gas industry (typical recovery from an oil field is 30% of the oil in place, the remaining 70% is tied up in wetting the reservoir rocks and near-field cohesive effects, replacing the fluid on the surface of the rocks would free up a bit of oil).

That was the last time I even thought about wetability. After reading the linked article I'm now wondering if you made a sphere hydrophillic you might be able to develop a field-rugged dehydrator.

You should be able tell from the above that I don't have a clue as to the answer to your question. It would be interesting to learn what you hear from the manufacturers.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
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[ivymike]

There's a company in the middle east (DIME) selling hydrophobic sand, which you can lay down under ponds / agricultural fields / etc to keep the water where you want it.

I think that applying a coating to rocks underground would be a bit more of a challenge than doing it to a piece of metal in a workshop, though...

So far I have a couple of answers back (quick response!) first one was "we get a lot of inquiries, so tell us every last detail about what you hope to do with our product, and we'll decide whether to get back to you (or just take your idea and run with it)" and second was "here's the pricing, let us know if that scares you off."

 

[Demon3]

Yes this can be done and I have done it. Search for super hydrophobic or ultra hydrophobic coatings. The patents were in the 1970s. This is old technology and the patents describe many ways to make them. It sounds great but has little real world applicability. Major companies have worked on it for decades. An example is Evonik (Creavis).

To get the effect all you need is something with low surface energy plus some roughness.

As an example, I took some spray paint randomly from a drawer in the lab, applied to stainless steel and while the paint was still wet dipped that into hydrophobic silica (Aerosil from Degussa). The hydrophobic silica particles imbedded in the paint and made it rough so you had a very hydrophobic and self-cleaning surface. Brilliantly hydrophobic, you could run water right off it even from a high pressure jet. Also made these by applying a hydrophobic organosilane to fabric (described in another thread here at Eng-Tips).

Many people assume these surfaces will reject ice. I checked mine and it didn't, ice stuck amazingly well to it. This may not be impossible though.

People assume they would be great e.g. in a dishwasher. They aren't as they don't work when surfactant is present. The surfactant makes the water wet the surface.

People assume they are great against dirt (Lotus Effect). They do work on dry dirt but greasy dirt wets and then the rough surface is harder to clean than a smooth one.

When at Electrolux I wrote a report on this explaining why the much hyped Lotus Effect doesn't work in the real world. Was fun making the surfaces though.

The main drawback is that these surfaces are damaged so easily. Once the roughness is affected they don't work.

Chris DeArmitt - PhD FRSC CChem
Plastic & Additives Webinars
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[KENAT]

Isn't ptfe hydrophobic, any chance that could work for you?

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[Demon3]

Just sand it and it will then be super hydrophobic due to the roughness.

Chris DeArmitt - PhD FRSC CChem
Plastic & Additives Webinars
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[patprimmer]

It's pretty hard to make PTFE stick to the substrate, but there is technology available from the cookware industry and from industrial coatings industry. DuPont and ICI (That division is now Asahi I think maybe?) where the leaders.

I used to deal with an industrial coater who applied PTFE to various surfaces maybe 20 years ago. I can check if he is still in business and has any info if you like. I am pretty shure though that his know how was straight out of ICI and DuPont product manuals.

Regards
Pat
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[VEBill]

What happens when they perfect superhydrophobic coatings, and then use it to paint a ship's hull?

 

[ivymike]

Lower friction and less fouling, apparently.

 

[btrueblood]

Aren't rabid dogs hydrophobic?

 

[ivymike]

Yes, but adhesion to metal is limited and their durability is rarely above a few hundred hours.