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Ice is hard and brittle – it would be surprising to bend an icicle around a softball and have it snap back to its original flat shape. But what the researchers did is, albeit on a much smaller scale.
They produced microscopic ice crystals that are not only elastic and flexible, but also transmit light quite well along their length. The research team suggested in a paper that these “ice microfibers” could one day be used to study air pollution. Published Thursday in the journal Science.
Limin Tong, a physicist at Zhejiang University in China, and his colleagues said they were inspired to work on ice after working with silica, a type of glass. Dr. Tong said everyday experience has taught us that glass in the form of windows or drinking bowls is fragile. But long, thin pieces of glass, such as fiber optic ribbons, are flexible. The researchers hypothesized that perhaps the same was true for ice.
Ice forms in a wide variety of natural environments such as glaciers and icebergs, but Dr. Tong and his colleagues needed to make frozen water that matched very specific properties. This ice had to be almost perfect.
The team started by making a circular chamber just over an inch in diameter on a 3D printer. Using liquid nitrogen, they cooled the space inside the chamber to negative 58 degrees Fahrenheit. They then placed small instruments, including a metal needle, with which 2,000 volts of electricity was applied to this miniature laboratory. This voltage created an electric field, and water molecules in the air reacted to the field by settling on the needle. Very slowly, at about one percent per second, rod-like ice microfibers grew from the tip of the needle.
The microfibers were never very long—they were barely visible to the naked eye—but high-resolution imaging revealed they were single crystals. This means that the atoms in them are arranged in repetitive patterns. Dr. “The atoms are arranged like a honeycomb,” Tong said.
Erland Schulson, an ice scientist at Dartmouth College, said that microfibers combined with their relative lack of microscopic defects (like tiny cracks, pores and missing atoms or molecules) make them much more flexible than naturally occurring ice. not included in the research.
“There are no grain boundaries, no cracks, nothing that limits the elastic stress that an object might otherwise experience.”
To demonstrate this flexibility, Dr. Tong and his colleagues used microscopic instruments to push the microfibers. They showed that ice could be bent in almost complete circles, like a cooked noodle, before returning to its original stick-like shape unchanged. “There was no permanent deformation,” Schulson said. A perspective article accompanying the study in the journal Science.
The team also found that the microfibers effectively transmit light along their length. When the researchers sent visible light to one end of the microfibers, more than 99 percent of it appeared at the other end. Dr. Tong said they function just like fiber optic wires that provide fast internet communication. “They can direct light from one side to the other.”
The researchers suggest that these microfibers could one day be used to study air quality. Particles associated with pollution – such as soot and metals – often stick to chunks of ice in the atmosphere, where they change the way the ice absorbs and reflects light. The team suggests that by building a microfiber out of dirty ice and examining how light propagates through it, it may be possible to better understand the amount and type of pollution in an area.
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