Making Ice Freeze at Room Temperature

[David Farber <dave () farber net>]

Begin forwarded message:

From: Dewayne Hendricks <dewayne () warpspeed com>
Date: May 5, 2006 12:28:34 PM EDT
To: Dewayne-Net Technology List <dewayne-net () warpspeed com>
Subject: [Dewayne-Net] Making Ice Freeze at Room Temperature
Reply-To: dewayne () warpspeed com

[Note:  This item comes from reader Randall.  DLH]

From: Randall <rvh40 () insightbb com>
Date: May 5, 2006 8:30:42 AM PDT
To: Dewayne Hendricks <dewayne () warpspeed com>
Subject: Making Ice Freeze at Room Temperature

<http://htdaw.blogsource.com/post.mhtml?post_id=322187>

Saturday, May 06, 2006 at 12:02 AM EDT
Ice freezes at room temperature

4 May 2006

Water has been found to form ice at room temperature if it is placed
between a tiny tungsten tip and a graphite surface. Joost Frenken and
colleagues at Leiden University in the Netherlands have found that the
water effectively acts like a glue in this situation, even though water
is normally thought of as a lubricant. The finding could be useful to
researchers studying micro- and nanoelectromechanical systems, which can
fail if the friction between the surfaces is too high (Phys. Rev. Lett.
96 166103).

Most surfaces are never smooth and completely flat. If two bodies are
brought together, they will not touch over the entire area of apparent
contact, but will rather touch over a large ensemble of tiny contacts.
Under normal, humid conditions, water vapour can condense out onto these
contacts, creating a tiny "capillary bridge". These bridges tend to make
the surfaces stick together and make it harder for them to slide over
each other.

The instrument

However, researchers have not been sure if this is also true when the
liquid is confined to small gaps between surfaces. To investigate this
problem further, Frenken's team carried out a series of experiments on
an instrument called a "tribolever", which uses tiny amounts of bending
inside a miniature silicon sensor to sense forces as small as 20
picoNewton.

The experiments involved attaching a sharp piece of tungsten wire onto
the sensor and carefully scanning it back and forth over the surface of
clean, high-quality graphite. The researchers found that icy nanoscale
water bridges -- lasting for several seconds -- formed between the two
surfaces at room temperature. In this geometry, the water effectively
acted like a glue, and not like a lubricant, joining the two surfaces
together.

"Our work provides a new understanding of what happens on the nanometre
scale between contacting and sliding bodies," says Frenken.

The team will now investigate using different materials for the tip and
substrate and varying other parameters like temperature and tip speed.
They will also study to what extent the ice contributes to friction
under practical circumstances.

About the author
Belle Dumé is science writer at PhysicsWeb

<http://physicsweb.org/articles/news/10/5/2/1>
Weblog at: <http://weblog.warpspeed.com>



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