Graphene’s “Invisible Touch”

Dearest galleons, today we’re going to explore one of those scientific studies that seems so strange it can’t possibly be true. And yet, SCIENCE! proves once again that the universe is much more complicated and bizarre than we observe in our day-to-day lives.

Graphene is the recent Nobel darling of the world of physics, and it has popped up in yet another experiment. Folks at Rensselaer Polytechnic Institute and Rice University used the ultra- thin nanomaterial in an experiment that looked at the wetting of solids.

Yes, you heard me. And for once, I’m not just making up words. “Wetting” is a thing.

But, more on that in a second. First, what exactly is graphene? Graphene consists of honeycombed carbon atoms arranged in a sheet resembling atomic chicken wire. It is the thinnest material known to scientists. Graphene has a lot of potential uses, particularly in electronics (it’s currently being looked at as the base for flexible electronic devices and screens, as well as exploiting some of its other properties for use in electronic cooling systems). Because it will almost certainly come in contact with water in any of these cases, it is important that we understand exactly how it interacts with water. Hence the study.

The researchers coated substances like gold and silicon with a single layer of graphene, then placed a water drop on the surface. What they found was that the water droplet seemingly ignored the graphene and acted almost exactly like it normally would on the particular surface.

Which may seem a bit confusing (it did to me at first glance). What’s so special about this? Before I give you the specifics of what makes this so interesting, we’re going to have to discuss wetting.

All wetting is is how water spreads on a solid surface. Water does not interact with all materials in the same manner, and wetting is the measurement of these differing interactions. Wettability (I swear, I’m not making that up) is calculated by placing a drop of water on a surface and measuring the angle at which the droplet meets the surface. On a hyrdophobic surface, the water balls up, leaving a steep angle. But if the surface loves water, the water spreads out and the angle shrinks.

Solid substances all have specific contact angles when a drop of water is placed upon them. What our researchers found was, even with that graphene sheet sitting snugly on top, the contact angle changed very little.

How can this be? To make it even more puzzling, let’s add this important piece into the mix: Remember how graphene is a carbon lattice? Well, that lattice is actually too fine for water to even get through (in fact, it’s impermeable- even a single proton can’t wiggle through).

That’s right- the water is having zero contact with the substance below the graphene. And yet, it’s acting like it is. For example, the contact angle for gold is 77 degrees. With the graphene applied, it’s 78 degrees. Silicon went from a normal 32 degrees to a graphene-enriched 33 degrees, and copper increased from 85 degrees to 86 degrees.

How can these contact angles be so similar when the water is never touching the gold or the silicon or the copper? Apparently, graphene is invisible to water, and the water is somehow able to sense the underlying material and acts as if the graphene isn’t even there.

…What the hell?

Applying more layers of graphene makes it less transparent, and after six layers the water no longer senses the underlying material and acts as if it’s on graphene. Which it is. And has been the entire time.

The reason the water can sense what lies beneath the graphene is thanks to van der Waals forces. See, water interacts with certain substances via non-bonding van der Waals forces (as opposed to the run-of-the-mill chemical and hydrogen bonds it makes with most substances), like a little form of atomic gravity. These van der Waals forces have a range of several nanometers. Which isn’t much unless we are dealing with something as mind-bogglingly thin as graphene. Because these single-atom-thick sheets of graphene (which are about 0.3 nanometeres thick) are all that stands between the two surfaces, the van der Waals forces are easily able to “see” through the graphene. Shoving more graphene between the surfaces finally puts enough distance between the surfaces that the van der Waals forces start seeing graphene instead of gold or silicon or copper.

Not only is this super cool, it’s also incredibly useful. Graphene can be used as a coating on metal to prevent oxidation without impeding the current interactions between the metal and water, allowing devices and machinery to operate for much, much longer without a complete reworking of their structure.

I have to say this is just about the most amazing little piece of physics I’ve read about in some time.

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