Conventional wisdom and the ice-cold instincts of Mortal Kombat's Sub-Zero tell us that water freezes at 0° C (32° F), but what if you add some creative science to the mix? Researchers in Switzerland have figured out a way to reduce the temperature of water to a very cool -263° C (-441.4° F) without freezing it, opening up some interesting possibilities around how we study molecular structures at extreme temperatures.
Water turns to ice as it is cooled to zero degrees and molecules on the surface begin to crystallize and turn to ice, which spreads to nearby molecules and continues on until the whole body of water is frozen solid. In this form, the water molecules are organized in a 3D lattice structure which is very different to the unorganized state of regular water molecules, a characteristic that allows it to flow freely.
So what if water could be cooled to below freezing temperatures without forming the icy crystals that give it this solidity? Physicists and chemists at ETH Zurich and the University of Zurich have figured out a new way of doing this, and it centers on a new kind of biological matter they've called lipidic mesophase. Within it are molecules that behave in much as the same way as natural fat molecules, or lipids, and will take it upon themselves to gather and self-assemble into membranes.
Those membranes then form a network of microscopic channels less than a nanometer across, and unfortunately for the would-be ice crystals, there's simply no room for them to form. This means that as water is added to the structure, it remains in its disorderly, flowing state even when cooled to extreme temperatures.
To see how far they could take things, the researchers took some liquid helium and cooled their lipidic mesophase structure to a chilly -263° C, which they note is just 10° C above absolute zero, with no sign of those dastardly ice crystals. This has ramifications beyond simply being a cool science experiment, as it could help us gain new understanding of how matter behaves at such extreme temperatures.
"In the normal freezing process, when ice crystals form they usually damage and destroy membranes and crucial large biomolecules, which prevents us from determining their structure and function when they interact with lipid membranes," explains Professor Raffaele Mezzenga from the Laboratory of Food & Soft Materials at ETH Zurich.
This is the very dilemma that motivated a similar line of research at the Massachusetts General Hospital last year, where scientists came up with a new supercooling technique that sealed the surface of water with a hydrocarbon-based oil. This prevented the water meeting air, which is where the first ice crystals form, and allowed them to store a sample of liquid water at -20° C (-4° F).
This kind of work opens up important possibilities for other researchers seeking to understand the structures and functions of natural molecules in different ways. It could also find uses in scenarios where it would be useful to prevent water from freezing, with airport runways one example to spring to mind.
"But our work wasn't aimed at exotic applications," Mezzenga says. "Our main focus was to give researchers a new tool to facilitate the study of molecular structures at low temperature without ice-interfering crystals, and ultimately to understand how two main components of life, i.e. water and lipids, interact under extreme conditions of temperature and geometrical confinement."
The research was published in the journal Nature Nanotechnology.
Source: ETH Zurich
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