| Nov 07, 2011 |
Tying atomic threads in knots may produce material benefits
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(Nanowerk News) A new generation of lighter, stronger plastics could be produced using an intricate chemical process devised by scientists.
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Chemists working on the nanoscale – 80,000 times smaller than a hair's breadth – have managed to tie molecules into complex knots that could give materials exceptional versatility.
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By weaving threads of atoms into the shape of five-point stars, researchers at the University of Edinburgh have created the building blocks of materials that could be supremely flexible and shock absorbent.
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They hope that the new molecules – known as pentafoil knots – will mimic the characteristics of complex knots found in proteins and DNA, which help to make some substances elastic.
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In natural rubber, for example, 85 per cent of its elasticity is caused by knot-like entanglements in its molecule chain.
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Creating knotted structures in the laboratory should make it easier for scientists to observe and understand exactly how entanglements influence a material's properties.
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And being able to produce materials with a specific number of well-defined knots, rather than the random mixture that occurs in today's plastics and polymers, scientists could exercise greater control when designing materials.
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The research, funded by the Engineering and Physical Sciences Research Council, is reported in Nature Chemistry journal ("A synthetic molecular pentafoil knot").
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The Edinburgh team, working with researchers from the University of Jyväskylä in Finland, is the first to create a knot with five crossing points.
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The pentafoil, also known as a Solomon's seal knot, has symbolic significance in many cultures and is the central emblem on the flags of Morocco and Ethiopia.
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Deliberately tying molecules into knots so that its properties can be studied is extremely difficult. Until now, only the simplest type of knot – the trefoil, with three crossing points – has been created by scientists.
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Remarkably, the thread of atoms that the Edinburgh team has tied into a five-star knot is just 160 atoms in length and measures a 16-millionth of a millimetre.
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Using a technique known as self-assembly, the researchers produced a chemical reaction in which atoms were chemically programmed to spontaneously wrap themselves up into the desired knot.
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Principal researcher David Leigh, Forbes Professor of Organic Chemistry at the University of Edinburgh, said: "It's very early to say for sure, but the type of mechanical cross-linking we have just carried out could lead to very light but strong materials - something akin to a molecular chain mail.
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"It could also produce materials with exceptional elastic or shock-absorbing properties because molecular knots and entanglements are intimately associated with those characteristics. By understanding better how those structures work - and being able to create them to order - we should be able to design materials that exploit those architectures with greater effect."
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