It seems hardly a day goes by without someone finding a way to make an
often inferior copy of what what one of God's many aliases, good ol'
Mother Nature, invented long ago.  This time, someone has come up with
artificial mother of pearl!!  See
http://www.newswise.com/articles/2003/5/SEASHELL.NSF.html?sc=wire for
the nifty-grifty details.  The article is not long, so i repeat it below:

Description: Researchers have developed a nanoscale, layered material
that comes close to nacre's properties, including its iridescence. The
ability to nanomanufacture artificial nacre may provide lightweight,
rigid composites for aircraft parts, artificial bone and other
applications. (Nature Materials, 25-May-2003)

ARLINGTON, Va. -- There is more to mother-of-pearl than good looks. Also
called nacre, the gleaming, white material is renowned in scientific
circles for its strong, yet flexible, properties. Now researchers have
developed a nanoscale, layered material that comes close to nacre's
properties, including its iridescence.
The ability to nanomanufacture artificial nacre may provide lightweight,
rigid composites for aircraft parts, artificial bone and other
applications.

Reporting online in Nature Materials on May 25, Nicholas Kotov and his
colleagues at Oklahoma State University and at Digital Instruments/Veeco
describe their method for creating nacre-like material that consists of
alternating layers of clay and a type of polymer called a
polyelectrolyte. Kotov received a National Science Foundation (NSF)
CAREER Award to pursue the work.

"The discovery allows researchers to tailor flexible materials to a
given application--to get the tough materials that nature has been able
to produce," said Lynn Schneemeyer, the NSF program officer who oversees
Kotov's award. NSF is an independent federal agency that supports
fundamental research and education across all fields of science and
engineering.

Natural nacre owes much of its strength and flexibility to an internal
brick-like structure. Protein layers only nanometers (billionths of a
meter) thick provide the pliable "mortar," while calcium carbonate, the
principal chemical in limestone and antacids, comprises the similarly
miniscule "bricks" adding hardness.

In the artificial nacre, platelets of a negatively-charged clay called
montmorillonite provide the bricks while fibers of a positively-charged
polyelectrolyte called poly(diallydimethylammonium) chloride (PDDA)
serve as the mortar. The opposite charges help the two components bond
tightly to form the nacre structure.

"The combination of montmorillonite and PDDA for nacre modeling came to
us quite naturally," said Kotov. "It was the very first
clay-polyelectrolyte system I worked with a few years back." He also
states that the montmorillonite has several advantages over other
layered minerals, such as talc, including an ability to disperse easily
in water, while the PDDA has a high affinity for clays.

Unique "sacrificial bonds" hold the polymer chains to each other in a
special way that maintains strength and flexibility. The bond is a
result of the polymer interacting with negative charges on the clay
surfaces (or, in the case of real nacre, proteins interacting with
positive calcium ions).

Such ionic bonds are strong and absorb energy when the artificial nacre
is deformed. If the bonds break, they can re-form when the stress goes
away. They are dubbed "sacrificial" because they take the brunt of an
attack, leaving the covalent bonds in the molecules intact.

The artificial nacre was created by immersing a glass slide in
alternating baths of clay and polymer. A robotic device performed the
200 dips, with each dip producing several plastic-clay layers--each clay
and plastic layer is, on average, only 24 nanometers thick.

"It is a very robust preparation and produces beautiful layers every
time," said Kotov.

Because of the artificial nacre's potential for high-strength,
protective coatings such as body armor and biocompatible substrates for
growing human tissue or organs, Kotov and his colleagues are working
with a company to further develop the material and techniques. And,
because researchers can easily add new components like ultraviolet
light- or corrosion-resistant chemicals to the artificial nacre, the
same manufacturing process can produce materials for a variety of
applications.

NSF PR03-60

NSF Science Expert: Lynn Schneemeyer, (703) 292-4945; [log in to unmask]

NSF Awardee: Nicholas Kotov, Oklahoma State University,
[log in to unmask]

From the Great, Chilly & Wet North (9 C and raining today!!),
Ross M.