X-Message-Number: 29865
From: "Basie" <>
Subject: 'Hot' Ice  (Water can freeze at high temperatures)
Date: Sun, 30 Sep 2007 00:11:22 -0400

'Hot' Ice Could Lead To Medical Device
Science Daily - Harvard physicists have shown that specially treated diamond 
coatings can keep water frozen at body temperature, a finding that may have 
applications in future medical implants.
Doctoral student Alexander Wissner-Gross (above) and Efthimios Kaxiras, 
Gordon McKay Professor of Applied Physics, have shown that treated diamond 
coatings can keep water frozen at body temperature. (Credit: Stephanie 
Mitchell/Harvard News Office)Ads by Google Advertise on this site
Doctoral student Alexander Wissner-Gross and Efthimios Kaxiras, physics 
professor and Gordon McKay Professor of Applied Physics, spent a year 
building and examining computer models that showed that a layer of diamond 
coated with sodium atoms will keep water frozen up to 108 degrees 
Fahrenheit.
In ice, water molecules are arranged in a rigid framework that gives the 
substance its hardness. The process of melting is somewhat like a building 
falling down: pieces that had been arranged into a rigid structure move and 
flow against one another, becoming liquid water.
The computer model shows that whenever a water molecule near the 
diamond-sodium surface starts to fall out of place, the surface stabilizes 
it and reassembles the crystalline ice structure.
Simulations show that the process works only for layers of ice so thin they're 
just a few molecules wide - three nanometers at room temperature and two 
nanometers at body temperature. A nanometer is a billionth of a meter.
The layer should be thick enough to form a biologically compatible shield 
over the diamond surface and to make diamond coatings more useful in medical 
devices, Wissner-Gross said.
The work is not the first showing that water can freeze at high 
temperatures. Dutch scientists had shown previously that ice can form at 
room temperature if placed between a tiny tungsten tip and a graphite 
surface. Kaxiras and Wissner-Gross's work shows that ice can be maintained 
over a large area at body temperature and pressure.
Device manufacturers have been considering using diamond coatings in medical 
implants because of their hardness. Concerns have been raised, however, 
because the coatings are difficult to get absolutely smooth, abrasion of the 
tissue surrounding the implant could result, and that diamond might have a 
higher chance of causing blood clots than other materials.
Wissner-Gross said a two-nanometer layer of ice would just fill the pits in 
the diamond surface, smoothing it out and discouraging clotting proteins 
from attaching to the surface.
"It should be just soft enough and water-friendly enough to smooth out 
diamond's disadvantages," Wissner-Gross said.
Wissner-Gross and Kaxiras are planning experiments to confirm the 
computerized findings in the real world. Wissner-Gross said they expect 
results within a year.
"We're reasonably confident we'll be able to realize the effect 
experimentally," Wissner-Gross said.
Wissner-Gross, who has been a doctoral student at Harvard since 2003, said 
the research grew out of an interest in the physical interaction of 
nanostructured surfaces with molecules that are biologically relevant, such 
as water. Diamond films are growing cheaper, Wissner-Gross said, and as 
their cost declines the array of possible uses of the material grows wider.
"We both had this notion that it would be very interesting to combine theory 
with respect to diamond surfaces with what's going on in cryobiology," 
Wissner-Gross said. "We were thinking about how we could leverage this 
long-term trend [of declining prices] to do something interesting in the 
medical field."

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