I know I said I was going to stop selfishly writing about graphene all the time, but then I stumbled across this paper called "Rebar Graphene" and became immediately intrigued. See, graphene is already known for having pretty spectacular mechanical properties — you've probably come across that totally nonsensical, but true-in-a-way statement about how if graphene were the thickness of plastic wrap then you could suspend it and an elephant could balance on a pencil which is itself balanced point-side-down on the graphene wrap and it wouldn't break. So how could I not be curious as to how they made it even stronger?
The answer, as it turns out, is my other favourite thing to over-write about, carbon nanotubes. Something to add to the ever increasing list of why they are interesting. The researchers used the nanotubes as reinforcing bars for the graphene in a manner analogous to the way rebar is used in concrete.
To get at why this is useful, we need to detour slightly into a graphene topic I haven't covered yet: how it's made. I'm sure I've brought up the Scotch tape thing before, but that is actually not a particularly practical way to make graphene for commercial applications. For making large areas of graphene, the current best method is to grow it at high temperatures on a copper surface. (The choice of copper is actually quite clever. It acts as a catalyst for growth so that once a monolayer of graphene has covered the whole surface, there's no more available catalyst and thus no more growth. It self-limits at a single layer.) But, there's a problem. How does one then get the graphene off the copper?
Generally, this is tackled by coating the graphene with a polymer for structural support and then dissolving away the copper leaving the graphene/polymer floating in a solution. Then you can just scoop it up with any substrate and clean off the polymer. But the ploymer can't be cleaned off completely and always leaves some surface contamination on the graphene. In some materials, surface contamination is not a big deal, but graphene is literally ALL SURFACE. So surface contamination matters a lot.
Enter rebar graphene. This stuff is so strong it can support itself without polymer! And, the electrical properties of the rebar graphene were not overly damaged by the incorporation of the nanotubes — the charge mobilities were still higher than those observed in silicon electronics, for example.
Carbon nanotubes: as always, making good things even better.
Check out the original paper, Rebar Graphene, at ACS Nano.
[Top image reprinted with permission from Yan et al.,Rebar Graphene, ACS Nano, Article ASAP, DOI: 10.1021/nn501132n. Copyright 2014 American Chemical Society]