Researchers say they have developed the world's strongest, lightest solids. Called aerogels, the sturdy materials are a high-tech amalgam of highly porous glass and plastic that is as light as air. In light of the events of Sept. 11 and a heightened interest in homeland security, these new materials show promise as lightweight body armor for soldiers, shielding for armored vehicles, and stronger building materials, the researchers say.
The materials could also be used for better window insulation, longer-lasting tires, and lighter, safer aircraft and space vehicles, they say.
A study describing these materials is scheduled to appear in the September 12 print issue of Nano Letters, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
"We took the lightest material available and made it 100 times stronger, giving us the strongest, lightest material known to man," says Nicholas Leventis, Ph.D., a chemist with the University of Missouri-Rolla and a chief author of the paper. "Our material appears promising for practically any application that requires lightweight, strong materials."
Aerogels were originally developed in the 1930s. They remained a curiosity until the 1960s, when scientists began to consider them as a medium for storing liquid rocket fuel. The first aerogels were made of silica and had a chemical composition identical to glass. Although lightweight, aerogels have, until now, been extremely brittle and have absorbed moisture easily, which limited their practical applications.
In an effort to improve upon the strength of these materials, Leventis and his associates decided to weave together strings of tiny particles of silica (glass) with polyurethane (a plastic. The resulting material, however, still remained too brittle.
The researchers then decided to cross-link (tie together chemically) the strings of the nano-sized glass particles with polyisocyanate, one of the two components of polyurethane. Like earlier aerogels, the resulting materials were almost as light as air. But the new chemical approach resulted in aerogels that were 100 times more resistant to breakage, and almost totally insensitive to moisture compared with the original version of aerogels made of plain silica.
Aerogels are also known for their high resistance to heat transfer, making them promising as insulating materials. In the near future, the new aerogel nanocomposites will probably appear in insulated windows, refrigerators and thermoses, Leventis predicts.
Other possibilities include more impact-resistant automobile bumpers and stronger, lighter armored vests. The new material can also store liquid fuel, making it useful for safer, more impact-resistant fuel tanks for aircraft and fuel transport vehicles. It can also be used for building lighter, more efficient frames for airplanes and spacecraft, according to the researchers.
The researchers have recently filed patents on their new aerogel technology. Leventis and his associates plan to make aerogels even stronger in the near future.
A few companies are developing aerogels commercially. Despite their fragility, some plain-silica aerogels are already in use on spacecraft to collect cosmic dust for analysis. They are also part of the instrumentation that measures radiation produced within nuclear reactors.
Funding for this research was provided by The Petroleum Research Fund, which is administered by the American Chemical Society.
Leventis' colleagues in this study were Chariklia Sotiriou-Leventis, Ph.D., and graduate students Guohui Zhang, and Abdel-Monem M. Rawashdeh.
Nicholas Leventis, Ph.D., is an associate professor of chemistry in the department of chemistry at the University of Missouri-Rolla.
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