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Carbon Jelly: C60's Latest Trick
Carbon soccer balls can form into gels all by themselves, say chemists, overturning the long-held belief that gels must consist of at least two chemical components.
Gels are something of a puzzle for chemists. These jelly-like materials are not quite solid and yet not liquid either. Gels live in a kind of chemical twilight zone where they share many properties of both phases of matter.
So confusing is this, that chemists find it hard even to define what it is to be a gel, or what properties its components must have.
One thing they agree on however is that gels consist of at least two components: a liquid component and a solid component that forms into a loose network which binds the substance together. This is how the jelly-like properties arise.
Now even that piece of common-lore might have to change. Today, Patrick Royall at the University of Bristol in the UK and Stephen Williams at the Australian National University say that C60, the soccer ball form of carbon, can form into a gel all by itself.
So how come? For some time, chemists have known that C60 forms several different phases of matter. It can be a solid crystal, for example. But it is also known to form into clusters of a wide range of sizes. And it can form a liquid over a limited range of temperatures (although whether this liquid is stable or not, nobody is quite sure).
The question that interests chemists is whether a liquid-like state can exist at the same as the clusters, which could then bind together forming the characteristic network structure that would hold the jelly-like substance together.
Royall and Williams answer this question by creating a computer model of this substance and then seeing whether it is stable. And their conclusion is that it can. “We have presented numerical evidence that C60, under the right conditions can form a gel,” they say.
Such a substance would be a bizarre chemical curiosity. It means that in addition to forming diamond, graphite, graphene and an infinite number of carbon chickenwire structures such as tubes and footballs, carbon can also be a jelly.
But there’s more work ahead. Knowing that a substance can be stable is obviously useful but that doesn’t mean that it’s possible to make it.
Royall and Williams say it should exist over the time scales that they can simulate–up to 100 nanoseconds.
But these kinds of simulations are notoriously difficult to fine tune. It’s possible that C60 might prefer to crystallise.
Of course, there’s only one way to find out. And now there’s likely to be no shortage of volunteers willing to try.
Ref: arxiv.org/abs/1102.2959: C60: the ﬁrst one-component gel?
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