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Wednesday, 17 August 2011

A new approach to scratch resistance

MIT News
Aug 17, 2011

A new way to analyze how coatings of tiny particles alter the properties of transparent plastic could help researchers create lightweight windows with nearly the strength of glass. The same method could also lead to high-strength, scratch-resistant coatings that could be applied to many different materials, according to the MIT researchers who developed the analysis.

The analysis used a polymer called poly(methyl methacrylate), or PMMA, which is widely used as a glass substitute. Known generically as acrylic, and sold under trademarks such as Lucite or Plexiglas, this material can be brittle and is far less resistant to scratching than glass.

Other researchers have added silica particles measuring just nanometers across to PMMA, creating a polymer-particle nanocomposite with much greater strength. But the MIT team, for the first time, has found a way to analyze the particle-polymer interactions of such coatings at the nanoscale, which could facilitate the discovery of improved coatings. Their work was reported in July in the journal Soft Matter.

The analysis was carried out by Meng Qu, a postdoc in MIT's Department of Materials Science and Engineering, along with Associate Professor of Materials Science and Engineering Krystyn Van Vliet and several researchers at DuPont Nanocomposite Technologies in Delaware. The work was partly funded by the DuPont-MIT Alliance.

Silica particles were used for the coating because they are transparent, so the finished material maintains its transparency. But silica and acrylic are not compatible, which would ordinarily cause clumping of the tiny silica grains — which measure only about 10 to 20 nanometers across, or about one ten-thousandth the width of a human hair. In order to overcome this, the silica was treated with other "functional groups" of molecules, changing its surface chemistry so it disperses evenly on the polymer surface.
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