Science Gazette

A scientist stretches the boundaries of when water will freeze

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Looks closely at the small frozen water droplets.

As he pushes the limits and obtains the finest look yet at small droplets of water freezing, an engineer is redefining everything we know about how water freezes.

Though it is one of science’s great mysteries, the transition of water into ice often passes people’s imaginations since it is just presumed to happen. But ice scientists like Hadi Ghasemi, Cullen Associate Professor of Mechanical Engineering at the University of Houston, are looking at how and why it occurs. Ghasemi has reported the best look yet into the process of crystallization of water into ice at the molecular level: water-ice phase change down to 2 nm (nanometers) in diameter.

Then Ghasemi found another finding when examining these small particles. By placing the small droplets in touch with soft surfaces like gels or lipids, he was able to breach the limit of when water freezes and keep them as liquid.

“We discovered that when a water droplet comes into touch with a soft interface, the freezing temperature is substantially lower than when it comes into contact with hard surfaces. In addition, if a few-nanometer water droplet comes into touch with a soft surface, it may prevent freezing to -44 C “Nature publishes an article by Ghasemi.

A water droplet’s freezing temperature limit is -38 C. That is, any water droplet will freeze at a temperature of 0 to -38 degrees Celsius. Until now, freezing was an unavoidable consequence of being below this temperature.

The act of freezing such a little water droplet is crucial for organisms’ survival in cold conditions, since a frozen water droplet within a cell causes the cell to burst and cause death. Climate forecast, cloud conditions, cryopreservation of organs, and technology vulnerable to icing conditions, such as airplanes and wind turbines, all benefit from the technique.

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“The problem of experimentally testing the freezing temperature of a few micrometer water droplet has remained unsolved. We were able to explore the freezing of water droplets from the micron scale down to the 2 nm scale using newly developed metrologies “Ghasemi said.

Previously, Ghasemi used a novel idea called stress localization to make an ice-repellent material for aeronautical purposes. His recent results aid in the study of natural phenomena and give guidance for the development of anti-icing systems for aviation, wind energy, and infrastructure, as well as cryopreservation systems.

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