Glassy polymer films that are 40% less dense and considerably more stable against ageing than standard acrylic glass are described online in Nature Materials this week. The new glasses may find use in nanotechnology and biomedical applications where polymer weight and stability are critical.To make the glassy films, Rodney Priestley and colleagues used a pulsed laser to gently evaporate molecules out of a frozen dilute solution of standard acrylic glass — poly(methyl methacrylate) (PMMA), which is widely used in automobiles, buildings and orthopaedic surgery. The evaporated PMMA molecules were deposited on a substrate and formed a film. Using atomic force microscopy, the authors found that unlike the unstructured standard PMMA glasses made by rapidly cooling the liquid, the new glassy films consisted of stable polymer nanoglobules. They propose that the globular nanostructure confers the lower density and higher thermal and kinetic stability — in particular, a 40-degree-higher glass transition temperature and a glass-to-liquid transformation rate a hundred times slower than standard PMMA glass.The authors also note that the fabrication of nanostructured ultrastable glasses from other polymers by pulsed-laser evaporation and deposition should be possible.
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