Figure 2
happens and how long it takes,” says Coveney. “Clay exists naturally as stacked sheets called tactoids. When you add a polymer, it will break up this natural configuration – encapsulating, exfoliating or intercalating the stacks. Our simulation showed that the composite then arranges itself in a particular orientation, such that the material properties begin to look very different from what you might predict from a linear combination of the properties of clay and the polymer.” The
paper was considered so important by
Advanced Materials that for the first time in its entire history the high impact journal published an extended feature so that the methods behind the work could be fully explained. “The ability to model and simulate the properties of a material in this manner has opened the door for making predictions that could vastly speed up many scientific discovery processes, not just in the field of clay-polymer nanocomposites,” explains Coveney. Graphene, for example, is a material that has
Figure 3
long been touted as a modern wonder material that will eventually revolutionise numerous fields of research. However, delivering the practical applications of graphene has proven difficult, not least due to the challenges of producing it in large enough quantities. Multiscale modelling could be used
to model the industrial production of
graphene by exfoliating 2D sheets of graphene from graphite – a process fairly similar
to the
exfoliation of clay tactoids in the production of clay-polymer nanocomposites. Coveney and his researchers have made extensive
use of Tier-0 PRACE supercomputers, including 40.5 million core hours on JUGENE BlueGene/P at FZJ. “Carrying out multiscale simulations comes under
the domain of what we call “heroic
Figure 2: Illustration of the dynamic process of polymer intercalation between the hexagonal clay layers. Each polymer molecule is a different colour and moves rapidly through the interlayer spacing
Figure 3: Coarse-grained molecular dynamics simulation of poly(vinyl) alcohol polymer intercalating between layers of clay
and time-consuming trial and error experiments can be eliminated from the discovery process. In
February 2015, the journal Advanced
Materials published a paper by Suter, Groen and Coveney that discusses the properties of a number of clay-polymer nanocomposites. However, it is not the specific materials that make the paper so interesting, but rather the groundbreaking methods behind the research. In the paper, they describe a method that can be used to calculate the properties of clay-polymer nanocomposites using multiscale modelling. The only inputs needed for this “virtual laboratory” are chemical composition, molecular structure, and processing conditions, and in return it provides information that has largely never been shown before in any kind of modelling, let alone in an experiment. “By connecting all the scales
together into a
multiscale model, we were able to show the process of polymers getting inside the clay layers – how it
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computing tasks”, he says. “I personally believe that the future of materials science lies in gaining a proper understanding of composites, and this is very much dependent on the high fidelity nature of our models and simulations. Tier-0 supercomputers such as those provided by PRACE are absolutely essential for running these simulations in feasible time periods, and so the success of our work and any future work that uses our methods leans on the access that researchers have to these valuable resources.” In the short term, the team’s methods have
the potential to speed scientific discovery and understanding. In the long run, materials science will be changed for the better, by eliminating a lot of the trial and error that currently besets the development of useful materials. ★
J. Suter, D. Groen, P. V. Coveney, “Chemically specific multiscale modeling of clay-polymer nanocomposites reveals intercalation dynamics, tactoid self-assembly and emergent materials properties”, Advanced Materials, 27 (6), 966–984 (2015), DOI: 10.1002/adma.201403361
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