When grown in tiny strands, ice can bend and then snap back into its original shape. These microfibres are the most flexible form of ice ever made.
Most water ice is extremely rigid and brittle, breaking easily rather than bending. However, a single long crystal of ice can be far more flexible. Limin Tong at Zhejiang University in China and his colleagues have used this fact to fabricate the most elastic water ice ever, close to the theoretical limit of how flexible it can be.
They made their fibres using water vapour piped into a small chamber kept at a temperature of -50° C. An electric field in the chamber attracted water molecules to a needle made of tungsten, where they crystallised to build fibres a few micrometres or less in diameter.
The researchers then cooled the ice even further, to between -70° C and -150° C and measured the elastic strain of the fibres, which is a measure of how much a material is being bent and deformed. They found that these fibres were more elastic than any other water ice structures that have been measured – some could even be bent nearly into circles, and all of them snapped back into straight lines afterwards.
“Previously, the largest elastic strain experimentally observed in ice was about 0.3 per cent, but now we have 10.9 per cent in ice microfibers, much more bendy than any ice before,” says Tong. The theoretical limit for the elastic strain in water ice is between 14 and 16.2 per cent.
When Tong and his team examined the ice strands in detail, they found hints of the presence of a second form of ice that is denser than the type of ice making up the majority of the fibres. The stress on the bent part of the fibre may have driven a transformation in the ice, which means these fibres could potentially help us understand how such transformations work.
The microfibres are extremely transparent, so they could be used to transport light, but their temperature requirements would make that difficult. For now, their main use is to study the small-scale physics of ice.
Journal reference: Science, DOI: 10.1126/science.abh3754
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