Springy ice crystals that bend without breaking offer scientists new insights into the fundamental properties of ice.

An image of six thin, yellow and white filaments arranged in parallel on a black background.  Each filament has a bright point of light of a different color above and below

Ice is known as a hard, brittle material. But researchers in China and the US have now made flexible ice microfibers that can bend without tearing. When the load is removed, the fibers quickly return to their original shape. The material undergoes unusual phase transitions when it is bent and can even transmit light just as efficiently as state-of-the-art on-chip waveguides.

The research team led by Xin Guo and Limin Tong from Zhejiang University produced the ice crystals using a growth method that was enhanced by an electric field. The fibers were grown from the tip of a tungsten needle at -50 ° C. By applying voltage to the needle, the team accelerated the diffusion of gaseous water molecules to the needle tip, which resulted in fibers over 400 μm in length growing in just two seconds. The crystals were hexagonal in cross section and were generally a few micrometers wide, although some were only hundreds of nanometers in size.

A picture of a series of thin needle-like spines growing from a central point at the bottom of the picture

The team tested the mechanical properties of the crystal fibers under colder conditions and found that the material can flex at an elongation approaching the theoretical elastic limit. When the fibers were bent, the team also observed an unusual, reversible phase transition as the material changed from a hexagonal crystal structure to a rhombohedral arrangement.

The absence of crystal defects allows the material to transmit visible light efficiently, which opens up its use as a flexible waveguide. The team concluded that the resilient crystals offer a new avenue for “exploring ice physics and opening up previously unexplored opportunities for ice-related technologies.”

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