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The Questionable Promise of Superhydrophobic Coatings

TUESDAY, MARCH 21, 2017

By Warren Brand

It was a handful of years ago that I was attending an industry conference. I was talking to a group of professionals, many of whom were folks who worked for a large chemical company that supplies base resins to coating formulators.

Base resins are those fundamental materials used to make finished paint and coating products. As flour is to donuts, cakes, and soups, base resins are to painting and coating materials.

Drinks had been had by all, and the tone was pleasant and open.

We were talking shop, and the chemists were talking about new formulations. Everyone was very excited about what I viewed as the very slightest of “improvements” in materials.

SH screen surface
Oak Ridge National Laboratory

Superhydrophobicity has some really cool characteristics and, at first glance, some serious potential for commercial or industrial applications.

I spoke up and inserted myself into the conversation and said, “Do you know what would happen if there was never an improvement or modification of paint systems again?”

They looked at me in anticipation. And I said: “Nothing. Not one thing would change within the industry.”

They didn’t laugh.

I explained that I saw these new improvements as, primarily, marketing tools, and that they did not really reflect fundamental technological improvements in coating technologies or performance. Nobody argued.

Then someone said, “Let’s keep that to ourselves,” and we all had a good laugh.

Which brings me to the current stone in my shoe: superhydrophobic paint systems. (I also have an issue with nano-technology, which I’ll address in another blog.)

If you haven’t heard the buzz, a quick search on Google reveals 418,000 results in 0.76 seconds. There are a bunch of really cool videos as well.

Understanding Superhydrophobicity

To save my fingers while typing, we’re going to abbreviate “superhydrophobicity” as “SH” from here forward.

SH is the degree to which water is repelled by a surface. And it can actually be measured and quantified by the shape of the droplet on the surface.

To be non-technical, the more round the droplet, the more hydrophobic. To be somewhat more technical, when the contact angle of the water droplet to the surface exceeds 160 degrees, it changes from hydrophobic to superhydrophobic.

In practice, it has some really cool characteristics and, at first glance, some serious potential for commercial or industrial applications. Imagine for a moment painting a surface that never gets dirty. Or one that’s perfectly cleaned whenever it rains or is simply rinsed down with water.

The marine industry and Navy would love to develop a viable SH system. Imagine a Navy, commercial or cruise ship that never gets dirty! The true Holy Grail would be under the water line: Imagine a coating that dramatically reduces the friction of water on the hull and is so slick that nothing (barnacles or other nasties) can stick to it.

Making a ship (or submarine) just a fraction of a percent more efficient and sleeker (with the reduction of friction) would increase speeds and reduce fuel costs dramatically. We’d be talking about savings of billions a year worldwide.

If a picture is worth a thousand words, then a video is worth, well, at least a thousand and one. Watching SH on a lotus leaf is mesmerizing:

Here’s a clip from a commercialized product showing a variety of cool, if contrived, examples of SH:

But Things May Not Be What They Seem

A few years ago, I was introduced to a young man and woman who had recently earned their MBAs from a prestigious Chicago-area business school.

They had purchased licensing rights to a new SH material invented and patented by one of the United States National Laboratories. Their license was very narrow, and included the interior lining of pipe systems. The math was stunningly encouraging: The more you removed the friction of a liquid flowing through a pipe (or the underside of a ship, as mentioned earlier), fittings and pump housings, the less power (electricity) needed and the more money saved. The potential savings in electricity in water, oil and the movement of other liquids were profound and encouraging.

A good friend had introduced me to the pair and they were considering hiring my consulting firm to assist in market development.

They were enthusiastic, animated and brilliant. The numbers, deck, analysis and presentation was flawless. However, the more they talked, the deeper the pit in my stomach grew.

They had been sold a bill of goods. They just didn’t know it yet–and it looked like I had to be the one to break the news.

The problem was, they had no understanding of how SH systems worked, and I knew from the first few minutes that this venture had no legs. They had wasted all of their time and money, and would continue to do so for several more weeks, until I insisted on a conference call with the doctor on the patent.

Coincidental Meetings

You see, it just so happened that, by pure coincidence, I had been invited to a technical marketing review only a few months earlier. I was flown to the East Coast and had to sign a ream of non-disclosure documents, so I need to be very delicate about what I share here.

I was brought into a large conference room, the far wall of which was lined with two-way mirrors. On the other side of the mirrors were a bunch of Ph.D.’s and marketing mavens. There were about 10 of us in the conference room, and, as I recall, I was the only one without a Ph.D. (I asked my host several times throughout the day if there hadn’t been some mistake and that, perhaps, there was another meeting up the hall of blue-collar painting types.)

For the next many hours, all we did was talk about SH materials and characteristics in marketing terms, but mostly technical application issues and long-term, durable characteristics.

It turns out, unless I’m missing something, or something new has come up, or someone has other insights (please comment on the blog), SH coatings will never work when submerged and, likely, will never be ready for prime time in large-scale commercial or industrial applications.

A Brief History of SH Coatings —And the Rub

The story goes, as I understand it, that scientists long knew about the amazing water-resistant characteristics of the lotus leaf:

Water magically hits the surface, but does not stick–at all.

Research began and coatings were developed. The problem, however, is that what creates SH is not the type of coating, or the way it’s applied, how hard of soft it is or anything else. It’s the microscopic pattern on the shape of the surface and its singular ability of this microscopic pattern to hold microscopic air packets in place.

Below is a diagram of a lotus leaf on the microscopic scale:

Lotus leaf
William Thielicke, CC BY-SA 4.0, via Wikimedia Commons

And here's a photo and atomic force microscopy depiction of a copper surface with a nanoparticle coating that renders it superhydrophobic:

Superhydrophobic copper place
AFM view of superhydrophobic surface
Galiya Magazova, CC BY-SA 4.0, via Wikimedia Commons

As you can see, the one thing the surfaces have in common is that, well, they’re pointy and/or raised. Why? Because they need to hold air.

Back to the two young, dynamic entrepreneurs whose wind I was about to remove from their sails.

I tried explaining this conceptual flaw to them, but I apparently lacked the credibility of the Ph.D. who sold them the license. They patiently and, somewhat condescendingly (my MBA in entreprenurship was only from De Paul) tried to explain that I clearly did not understand the situation.

Finally, I suggested a conference call. I said, “You’re right. Perhaps I’m missing something. Maybe the doc can help me understand.”

They thought that was an excellent idea.

After the normal pleasantries and introductions, the conversation with the chemist went something like this.

Me: “So, my understanding of SH is that you have this very tiny matrix on the surface of the material which holds these tiny air bubbles which provide the SH.”

Him: “Yes, that’s basically correct.”

Me: “So help me understand how the small air bubbles are going to stay in place underwater and continue to provide SH?”

Him: “Um, well, you see…” and he went into highly technical details that had no relevance to the question I had just asked.

I continued to press him, and he finally said something like:

Him: “Well, we might be able to modify the material and introduce an oil of some type onto the surface.”

The students finally got it. And I never heard from them again, despite my repeated follow-ups.

Can They Ever Work?

There’s a lot of publicity, articles and, apparently, money being spent developing these types of materials, but I fail to see how they are ever going to work in commercial or industrial applications for two reasons:

1. Those tiny ridges and points are really good at holding air, when they’re clean. What happens when they get dirty? No more SH. I’ve not seen any data or research to show how it’s possible to keep these highly delicate surfaces clean.

2. The surfaces I’ve seen are thin, soft and delicate. Because the microscope structure needs to retain that fine pattern, it is, by definition, delicate.

I’m hoping I’m wrong about SH materials. A big part of what my technical consulting firm does is identify optimal corrosion mitigation (and optimal beautification solutions) and write site-specific, application-specific application specifications. I absolutely love being introduced to new and exciting materials, which benefit our clients.

I’m very much looking for comments to this blog. Fundamentally, I want to learn as much as I can to better service owners. Isn’t that why we’re all here?

ABOUT THE BLOGGER

Warren Brand

Warren Brand’s coatings career has ranged from entry-level field painting to the presidency of two successful companies. Over nearly three decades, he has project-managed thousands of coating installations and developed specs for thousands of paint and coating applications. NACE Level 3 and SSPC PCS 2 certified, Brand, an MBA and martial-arts instructor, now heads Chicago Corrosion Group, a leading coatings consultancy. Contact Warren.

SEE ALL CONTENT FROM THIS CONTRIUBTOR

   

Tagged categories: Coating chemistry; Specialty Coatings; Water repellents

Comment from Tom Schwerdt, (3/22/2017, 9:18 AM)

Warren, That's been pretty much my exact analysis of SH materials. When they get brought up, I typically will first ask "Okay, how durable is this one?" and get some hemming and hawing. SH is a great property, I just have never seen a version that will stand up to actual use for a reasonable timeframe.


Comment from Warren Brand, (3/22/2017, 10:50 AM)

Hi Tom, Agreed. Perhaps there's something new in the marketplace that we're not aware of. If so, I hope someone posts.


Comment from Gregory Berg, (3/22/2017, 1:12 PM)

I went so far as to speak with one of the companies working on SH regarding an industrial application. I was actually told the system was in development for industrial applications and I would be contacted to be a potential tester for the product. That was 5 years ago and I have not heard anything since even with a follow up inquiry by me.... Ill believe it when I see it


Comment from Anthony Nicholas, (3/22/2017, 2:25 PM)

Great article and tone Warren. Its refreshing to read such a well written non bias take on the tech. We all want it to be true but all I have ever had are marketing guys or people new to the business trying to push this stuff. I still have seen no real life industrial type solutions actually in place and working, its been 4 or more years now and all is quiet again! Perhaps its still emerging and on its way. Hope so too.


Comment from M. Halliwell, (3/23/2017, 11:40 AM)

Warren, you hit the nail on the head. Whether is it SH or some of these super-stick nano surfaces (like the "gecko gloves" ones that were supposed to make your average Joe able to climb a wall like Spiderman), nano materials have a long way to go to be durable and remain clean enough to maintain the miraculous properties they display when new. Until then, the hype is fun to listen too as long as you remember the reality of these products.


Comment from Warren Brand, (3/23/2017, 5:49 PM)

Hi All, Thanks very much for sharing your thoughts. I know you're all busy and appreciate the input. I also think the silence from those promoting SH materials speaks volumes.


Comment from edward telson, (3/24/2017, 2:23 PM)

As one who promotes SH on architectural substrates the title of the blog can be misleading indicating that SH is not all it should be in all realms which is not true. It is true in your argument that below water your analysis is correct however surfaces above water and the pronounced cleaning effects on architectural substrates is well demonstrated with SH and a history over a decade with millions of square feet. So SH does have a real value proposition on architectural substrates. . And as having been a contractor, son of a coatings contractor and now in manufacturing as one of those who promote SH I can unequivocally say it works. Perhaps it would be better to distinguish between industrial application of SH and architectural in the title as it can appear misleading.


Comment from Warren Brand, (3/25/2017, 3:10 PM)

Hi Edward, thank you very much for taking the time to respond. I'm always open to being corrected! What specific products are you referring to? Can you please provide case studies? Calling my assertions "not true" is a bold statement and I'll be the first to agree with you, as soon as you are able to provide data supporting that millions of square feet of SH coatings have been applied for over a decade. If this site prevents you providing specific material information, please email that to me directly at warren@chicagocorrosiongroup.com . Otherwise, generic descriptions of materials would be great! Hope you respond soon. Eager to be educated and continue the conversation. Sincerely, Warren


Comment from Warren Brand, (3/28/2017, 7:02 PM)

Hey Ed. Any news? Eager to hear.


Comment from Chander Patil, (3/29/2017, 10:21 AM)

Warren, you should also check out on TED a demo and explanation of SH coatings.


Comment from Warren Brand, (3/29/2017, 11:06 AM)

Hi Chander. If it's the one I'm thinking about, it's similar to the video embedded here.


Comment from Chander Patil, (3/29/2017, 11:12 AM)

No, It is TED talk show by Mark Shaw The title is "One Very Dry Demo" Feb 2013. To me this is a very interesting topic and potentially great advancement in coating science. The other commercial application is LiquiGlide developed at MIT


Comment from Warren Brand, (3/30/2017, 11:02 AM)

Hi Chander. I know Mark. Great guy. The video embedded in my blog is his product. I Googled LiquiGlide. All SH materials, by definition, do the same thing. I think, however, LiquiGlide has a unique niche - in one-time use containers. Also, from their video, it looks like most of the products they reviewed were thicker, katsup, gels, etc., - which makes sense. Thinner materials, I would imagine, would be more likely to remove the small air bubbles which provide SH. I am 100% certain that SH materials will enter the mainstream in certain, specific roles. The point of my blog was that I don't see how they will ever be ready for large-scale use in commercial, architectural or industrial applications where they will be exposed to dirt, grime, and the elements in general.


Comment from Stephen Gressel, (6/30/2017, 9:39 AM)

Well that's a drag (no pun intended) Warren. I was hoping I would eventually be able to coat drainage systems with this stuff and keep dirt, etc., from clogging them up. Guess it was just a pipe dream (pun intended that time).


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