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Nanocomposite Mimics Nacre’s Weight, Strength and Stretch
 Nanocomposite Mimics Nacre’s Weight, Strength and Stretch 7/23/2008 Researchers in Switzerland said they have created a composite material that combines the strength of ceramics with the lightweight and stretchability of polymers. The new material could lead to more durable bone and dental implants, more fuel-efficient cars and airplanes and, even, they say, bendable and transparent electronics. Created by dispersing tiny platelets of aluminum oxide in a polymer, the new material is reportedly five times stronger than a similar material developed earlier by MIT and much less brittle than a clay-reinforced polymer introduced by University of Michigan researchers in 2007, said Ludwig Gauckler, the professor of materials at the Swiss Federal Institute of Technology Zurich, who led the new hybrid’s research. Gauckler indicated that a film of the hybrid is as strong as aluminum foil. If stretched, the material can expand up to 25 percent, while foil will break at two percent. Harvard materials scientist, Andre Studart, also worked on the project. According to Studart, the material is “as strong but half to a quarter lighter than steel.” He explained that the material’s strength comes from platelets being diffused throughout the new hybrid. "It will be strong in two directions and not only in one direction, as is the case of fiber-reinforced material," he said. While the material Gauckler and Studart developed was translucent, they noted that its structure could be modified to render it transparent, making it suitable for dental material and transparent electronic circuits. Material Mimics Nature The nanocomposite was created by dispersing aluminum oxide platelets in ethanol and spreading the mixture over water’s surface, where they self assembled into a single layer. The researchers then dipped a glass plate into the solution, transferring the platelets to glass. The final step entailed depositing a layer of the biocompatible polymer chitosan on top of the platelets. This process was repeated until the thickness of the final composite was “a few tens of micrometers,” Gauckler said, at which point the researchers peeled it off the glass plate with a razor blade. The researchers said they designed the material by studying the mechanical structure of nacre, the shiny layer that appears on the inside of seashells. They found that nacre is comprised of calcium carbonate platelets arranged in layers inside a protein-based polymer. "There's something very special about the size of these platelets," Studart said. "Nacre uses specific platelet length and thickness to achieve the high strength and [stretchability] that you see in metals." He noted that the ratio between the length and thickness of the platelets, “has to be just right. If it is too high, the platelets break when the material is stretched. If it is too low, the material is not strong enough.” The researchers say they chose to work with aluminum oxide platelets, which are five times as strong as nacre’s calcium carbonate platelets. To lower the likelihood of flaws in the material’s structure, they also made their platelets thinner – about 200 nm across, as opposed to the 500-1,000 nm width of nacre’s naturally occurring platelets. More Work Needed Asked to comment on the new hybrid’s development, Francois Barthelat, a mechanical-engineering professor and materials researcher at McGill University in Montreal, Quebec, said he believed the nanocomposite “is the closest anyone has come to duplicating the mechanical structure and behavior of a natural material.” Barthelat added, however, that the researchers would have to develop a faster way to manufacture large quantities of the nanocomposite before it could be used commercially. Gauckler admitted that many improvements would be required before the material would have practical applications. He said a better polymer would make the composite stronger and an improved method of bonding the aluminum oxide and polymer also needed to be found. For now, however, the researcher said he is satisfied to know that "we have shown we can [come close to] doing as good a job as nature." << Back to News Join our online discussion forum and comment on this article!
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