Team tie world's smallest knot

12 January 2017
Posted by Chris Smith.

At ten thousand times smaller than a human hair, chemists in Manchester, England, have tied the world's tiniest and tightest knot in a string of atoms. Most people are familiar with bending down to tie a shoelace, but not normally on the atomic scale.

What David Leigh and his colleagues have achieved is not only a world first and a world record, but also opens the door to a field of nano-weaving that will produce complex new fabrics with a rich range of properties.

Their "shoelace" is actually a string of 192 mainly carbon atoms link to form a chain measuring about 20 nanometres - one fifty-thousandth of a millimetre - long. The knot they tie in it resembles a 4 leaf clover with the free ends linked together to form a closed braid in which the strands cross over themselves 8 times.

The team made the molecular tangle in a test tube using a sequence of carefully-controlled chemical reactions. Starting with 4 short pieces of atomic "string" dissolved in a suitable solvent, iron catalysts are added which sequentially bend the strings into the correct configurations and introduce the correct twists into the molecules before ultimately joining the ends together.

The structures are to small to physically "see", so instead the team used the way in which the knot interacts with light to confirm that they really had stitched up a world record.

It's also not a quick knot to tie: the whole process takes more than two days using the method that the team have published in the journal Science this week. But, as Leigh points out, being able to manipulate molecules in this way and at this scale will enable researchers to explore new methods to fabricate materials with special new properties that can be also be stretched in multiple directions.

"Look at Kevlar. This super-strong plastic is used in bullet proof vests. At the molecular level it consists of straight rods packed tightly together like pencils in a pencil box. What we might be able to do is actually use these new techniques to weave materials like that to get something that is much lighter but even stronger..."

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