Water ice isn’t exactly known for its flexibility. In fact, it’s quite the opposite: rigid and brittle, easily fracturing and snapping. It’s why avalanches and sea ice fragmentation occur.
It’s also why new research is so fascinating. Scientists have just grown microfibers of water ice that can bend in a loop – breaking the previous maximum strain by a significant percentage and opening up new opportunities for the exploration of ice physics.
Ice doesn’t always behave the way we expect, and its elasticity – or rather, lack thereof – is a perfect example. Theoretically, it should have a maximum elastic strain of around 15 percent. In the real world, the maximum elastic strain ever measured was less than 0.3 percent. The reason for this discrepancy is that ice crystals have structural imperfections that drive up their brittleness.
So a team of researchers led by nanoscientist Peizhen Xu of Zhejiang University in China sought to create ice with as few structural imperfections as possible.
The experiment consisted of a tungsten needle in an ultracold chamber, sitting at around minus 50 degrees Celsius, much colder than has been previously attempted. Water vapor was released into the chamber, and an electric field was applied. This attracted water molecules to the tip of the needle, where they crystallized, forming a microfiber with a maximum width of around 10 micrometers, smaller than the width of a human hair.
The next step was to lower the temperature to between minus 70 and minus150 degrees Celsius. Under these low temperatures, the researchers tried bending the ice fibers.
At minus 150 degrees Celsius, they found that a microfiber 4.4 micrometers across was able to bend into a nearly circular shape, with a radius of 20 micrometers. This suggests a maximum elastic strain of 10.9 percent – much closer to the theoretical limit than previous attempts.
Even better, when the researchers released the ice, it sprang back into its previous shape.
Although ice might look the same to us, its crystalline structure can vary quite a bit. Each configuration of molecules in an ice crystal is known as a phase, and there are quite a number of these phases. Transitions between phases can occur under a variety of conditions that have to do with pressure and temperature.
With their bendy ice, the team noted such a phase transition, from a form of ice known as ice Ih, the hexagonal crystal form of ordinary ice such as is found in nature, to the rhombohedral form ice II, which is formed by compressing ice Ih. This transition occurred during sharp bends of the ice microfiber at temperatures lower than minus 70 degrees Celsius and was also reversible.
This, the researchers noted, could offer a new way to study phase transitions in ice.
Finally, the team tried using their near-perfect ice as a waveguide for light, attaching an optical light to one end of the microfiber. Multiple wavelengths were transmitted as effectively as state-of-the-art on-chip waveguides such as silicon nitride and silica, suggesting that ice microfibers could be used as flexible waveguides for optical wavelengths at low temperatures.
“We could imagine the use of IMFs as low-temperature sensors to study, for example, molecular adsorption on ice, environmental changes, structural variation, and surface deformation of ice,” the researchers wrote in their paper.
“In short, the elastic ice microfibers demonstrated here may offer an alternative platform for exploring ice physics and open previously unexplored opportunities for ice-related technology in various disciplines.”
Very freaking cool.
The research has been published in Science.