[ad_1]
Water ice isn’t exactly known for its flexibility. In fact, it is quite the opposite: stiff and brittle, fracturing and breaking easily. This is why avalanches and sea ice fragmentation occur.
This is also why the new research is so fascinating. Scientists have just grown water ice microfibers that can bend into a loop – breaking the previous peak stress by a significant percentage and opening up new opportunities for exploring the physics of ice.
Ice doesn’t always behave as expected, and its elasticity – or rather the lack of it – is a prime example. Theoretically, it should have a maximum elastic strain of around 15 percent. In the real world, the maximum elastic stress ever measured was less than 0.3 percent. The reason for this discrepancy is that ice crystals have structural imperfections which increase their fragility.
Thus, 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 ultra-cold chamber, sitting at about minus 50 degrees Celsius, much cooler than what had been attempted previously. Water vapor was released into the chamber and an electric field was applied. This attracted the water molecules to the tip of the needle, where they crystallized, forming a microfiber with a maximum width of about 10 microns, smaller than the width of a human hair.
The next step was to lower the temperature to between minus 70 and minus 150 degrees Celsius. Under these low temperatures, the researchers tried to bend the ice fibers.
At minus 150 degrees Celsius, they found that a microfiber 4.4 micrometers in diameter was able to bend into an almost circular shape, with a radius of 20 microns. This suggests a maximum elastic strain of 10.9 percent – much closer to the theoretical limit than previous attempts.
Better yet, when the researchers released the ice, it returned to its previous shape.
Although ice may look like us, its crystal structure can vary widely. Each configuration of molecules in an ice crystal is known as a phase, and there are a number of such phases. Transitions between phases can occur under various conditions related to pressure and temperature.
With their curved ice, the team noted such a phase transition, from a form of ice known as Ih ice, the hexagonal crystalline form of ordinary ice as found in nature, to the rhombohedral ice form II, which is formed by compressing ice Uh. This transition occurred during tight turns of the ice microfiber at temperatures below 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 to use their near-perfect ice as a waveguide for the light, attaching an optical light to one end of the microfiber. Multiple wavelengths were transmitted as efficiently as advanced on-chip waveguides such as silicon nitride and silica, suggesting that ice microfibers could be used as flexible waveguides for lengths of low temperature optical wave.
“We could imagine using MFIs as low temperature sensors to study, for example, molecular adsorption on ice, environmental changes, structural variations and deformation of the ice surface,” the researchers wrote. in their article.
In short, the elastic ice microfibers presented here may offer an alternative platform to explore the physics of ice and open up previously unexplored opportunities for ice-related technology in various disciplines.
Very cool.
The research was published in Science.
[ad_2]
Source link