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NewsLife-sized clayMoving easily among systems of the TeraGrid and two European grids, researchers find never-before-observed properties of clay particles used in novel nanocomposites. Download a pdf of the print version.
Visualization of a clay system containing approximately 10 million atoms after 0.5 nanoseconds of simulation. The system is 0.3 microns wide by 0.2 microns deep by 2.5 nanometers high. The vertical dimension is expanded to allow visualization of thermal sheet fluctuations. Atoms are colored: Mg (green), Al (blue), O (red), Si (gray), Na (yellow), H (white). Image courtesy of Peter Coveney. In the late '80s, Toyota patented a nanocomposite material made of nylon interspersed with layers of a common clay called montmorillonite. The result is a light, strong material that offers improved performance (and recyclability) at significantly less weight. It's a great material for car design. And that's just the beginning. Since Toyota's announcement, says theoretical chemist Peter Coveney of University College, London, nanoscale application of clay has fired the imagination of many researchers. "The clay confers remarkably enhanced material properties to the original polymer, like mechanical strength and barrier properties, such as to prevent diffusion of gases and to act as a flame retardant. There are many applications for these novel materials." The key is to better understand how clay particles behave at the nanoscale, in particular to control how they "exfoliate"-scatter from layered arrangements, like cards stacked one on top of another, into individual nanometer thick sheets that can be dispersed within a matrix of polymer. Previous simulations have been limited to system sizes in the range of 10,000 atoms-much smaller than the realistic size of the clay particles and too small to observe many physical properties of the material. 
Visualization of a sodium clay system containing 263,750 atoms after about one nanosecond of simulation. The simulation cell is 450 x 260 x 24.1 angstroms. The vertical dimension is expanded 15 times to aid viewing. Bending of the clay sheets and roughness of the clay surface are clearly visible. Arrows indicate the surface of the clay layer near adsorbed sodium ions, where oxygen atoms protrude further into the interlayer spacing than the surrounding clay surface atoms. Atoms are colored: Mg (green), Al (blue), O (red), Si (gray), Na (yellow), H (white). Image courtesy of Peter Coveney, University College, London. Using TeraGrid systems at TACC, NCSA and PSC in a "federated grid" with systems at the UK National Grid Service and the EU Deisa grid, Coveney and colleagues did extensive simulations of clay particles in system sizes that range up to 10 million atoms. Employing innovative middleware his UK team developed, called the Application Hosting Environment, the researchers moved with ease among the three different grids. At large system sizes-up to three orders of magnitude larger than prior work-the simulations approached the realistic size of clay "platelets." The results (reported this year in the Journal of Physical Chemistry C) revealed thermally-induced undulations in the clay sheets not before observed, findings that make it possible to calculate elastic properties (such as the bending modulus) difficult to obtain experimentally. "Because we've been able for the first time, to approach the dimensions of real-life clay platelets," says Coveney, "we expect to use the high-performance grid-computing infrastructure we've exploited with this work to capture other effects that arise in these clay-polymer nanocomposites."
Peter Coveney, University College, London. More information |
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