Undulating clay

A UK computer simulation has revealed that, at a certain size, microscopic sheets of clay start to undulate, something that has never been observed in the material before.

The effect emerged from some of the largest computer simulations ever attempted which required the pooled resources of supercomputers on three grids across two continents.

The research is expected to provide insights into the properties of an important class of new materials, clay polymer nanocomposites, which are under investigation for many applications, for example as materials for use in car bodies.

Supercomputers on the UK National Grid Service, the US TeraGrid and DEISA (EU Distributed European Infrastructure for Supercomputing Applications), linked by dedicated high speed optical networks including UKLight, were pressed into service.

Prof Peter Coveney and colleagues from University College London (UCL) used these resources to produce simulations of five computer models of the platelets that lock together to form clay sheets, the difference between each model being its size and complexity.

Each model simulated accurately the motion and interactions between all the atoms in two sheets of clay separated by a layer of water and sodium ions. In the largest model, the motions of nearly 10m atoms were taken into account. The simulations were run over timescales of up to 2nsec.

Data from the simulations were returned to computers back at UCL for visualisation which  revealed the undulations. 'As we moved from smaller to larger models we began to see collective undulations – the clay platelet sheets fluctuate up and down,' said Prof Coveney.

This property, which was not known before in clay materials, is on too small a scale to be easily verified by experiment. But it has implications for the properties of clay on an ordinary scale which can be computed and then compared with experiment. For example, the team has used the response of the clay sheets to the undulations to calculate their elasticity (or Young’s modulus).

As a next step, the group plans to simulate clay platelets embedded in a polymer matrix. Such clay-polymer nanocomposites are under investigation for a number of applications ranging from car bodies and other automotive uses, through oilfield technology to drinks packaging.

Compared with polymers alone, they have far greater mechanical strength, improved fire retardant properties and they make better barriers to the diffusion of gas. 'These simulations will give us a better understanding of the properties of these new and important materials,' said Prof Coveney.