Chemical process could lead to lighter and stronger plastics

Edinburgh University scientists have devised a chemical process that could produce lighter, stronger plastics.

The team, which has been working in conjunction with researchers at Finland’s Jyväskylä University, has managed to tie molecules at the nanoscale into complex knots that could give materials increased versatility.

David Leigh, principal investigator from Edinburgh University, told The Engineer: ‘We have succeeded in tying a molecule into a pentafoil knot — the most complex knot yet made with a molecule.’

The team is optimistic that the pentafoil knots will mimic the characteristics of the complex knots found in proteins and DNA, which help make certain substances elastic.

‘Any scientist could replicate what we have done by following the recipe we discovered using the special chemical building blocks we developed,’ explained Leigh.

Being able to produce materials with a set number of well-defined knots could provide scientists with greater control when they are designing new materials.

Leigh said: ‘Knots and entanglements in molecules are responsible for the elastic properties of rubber and plastics. So by being able to design molecules with particular knotted structures we may be able to make materials and plastics with improved elastic or shock-absorbing properties.

‘These could be useful in anything from space craft and body parts to bullet-proof vests.’

The thread of atoms that was tied into a five-star knot was 160 atoms long and measured a 16-millionth of a millimetre.

The researchers used a technique known as self-assembly, which produced a chemical reaction in which atoms were chemically programmed to spontaneously wrap themselves into the desired knot.

‘One of the most difficult things was — after obtaining the molecular knot — proving its knotted structure. We did this by a technique called X-ray crystallography that determines the exact position of the atoms in the molecule. This requires a very regular crystal of the knot, which took more than a year to obtain,’ said Leigh.

The Edinburgh team is the first to produce a knot with five crossing points. Until now, only scientists have created the simplest type of knot, the trefoil, with three crossing points.