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Scientists freeze water with heat | In what is a bizarre trick, scientists have come up with a way that can make water freeze solid as it's heating up. Popular belief contends that water freezes at 32 degrees Fahrenheit (0 degrees Celsius). Now, according to a report in Live Science, researcher Igor
Lubomirsky at the Weizmann Institute of Science in Rehovot, Israel, and his colleagues
have discovered another way to control the freezing point of water - via what
are called quasi-amorphous pyroelectric thin films. These surfaces change their
electrical charge depending on their temperature. When pyroelectic surfaces are
positively charged, water becomes easier to freeze, and when they have a negative
charge, it becomes harder to freeze. The researchers saw that supercooled water
could freeze as it's being heated, as long as the temperature changes the surface
charge as well. For instance, when supercooled water is on a negatively charged
lithium tantalate surface, it will freeze solid immediately when the surface is
heated to 17.6 degrees F (minus 8 degrees C) and its charge switches to positive.
Curiously, positively charged surfaces inspire supercooled water to freeze from
the bottom up, while negatively charged surfaces cause it to freeze from the top
down. This likely has to do with how water molecules orient themselves - the negatively
charged oxygen atoms in water molecules naturally point toward positively charged
surfaces, while the reverse is true with hydrogen atoms. "The difference between
the positive and negative charge was unexpected," Lubomirsky said. The ability
to better control the freezing temperature of supercooled water could be critical
for a variety of applications, including the survival of cold-blooded animals,
the cryo-preservation of cells and tissues, the protection of crops from freezing,
and the ability to understand and trigger cloud formation. |
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