Languorous Liquids

Upcoming experiments planned for the International Space Station will help engineers on Earth learn to handle undercooled fluids.

High-performance golf clubs. Ultra-sharp knives. Superior fiber optics for telecommunications. Tough, lightweight materials for future spacecraft.

What do all these things have in common? They can all be made using "undercooled" liquids: molten materials that are cooled below the normal freezing point yet, through special handling, are kept in a liquid state.

By avoiding normal freezing, one can coax the liquid into becoming a very different kind of solid. In normal freezing, the molecules of the liquid settle into an orderly crystalline grid, like soldiers falling in line. This is how ice, normal metals, and indeed most solids are formed. Undercooled liquids solidify in a different way. As they cool, they thicken and eventually stop flowing - like a liquid "on pause." The result is a solid whose molecules remain scrambled in a semi-random, amorphous arrangement. This molecular structure, most commonly found in window glass but possible in metals, too, has special properties. Amorphous metal alloys, for instance, can be twice as strong and three times more elastic than steel.

There's great potential for products made from these liquids, but they are notoriously difficult to handle.

An undercooled liquid is a delicate, unstable state of matter. It desperately "wants" to crystallize into a normal solid. All that's needed is a place for the crystallization to begin - such as the crystalline surface of a container wall or even a speck of dust - and the liquid will suddenly freeze solid. In other words, working with undercooled liquids is a bit like juggling mousetraps: they're prone to suddenly "snap" and ruin the trick.

Image courtesy Liquidmetal Technologies. A few of the things manufacturers can make better using undercooled fluids.

Remarkably, manufacturers on Earth have managed to make some products from these liquids anyway: computer components, golf clubs, tennis racquets. There's even a solar wind collector on board NASA's Genesis spacecraft made of undercooled amorphous metal.