Scientists demystify behaviour of glass

August 4th, 2008 - 4:02 pm ICT by IANS  


Sydney, Aug 4 (IANS) Two scientists are one step closer to explaining the nature of glass and its transition from liquid to solid, says a study. Peter Harrowell and Asaph Widmer-Cooper, theoretical chemists from the School of Chemistry along with colleagues from Columbia University, have been studying the transition of a fluid into a rigid glass in an attempt to understand stress relaxation in a disordered state.

“Glasses are the most viscous of liquids and the most structureless of solids” said Harrowell. “As such, glasses represent the most poorly understood features of both states of matter. That makes them a really profound puzzle.”

One of the most important insights to have emerged over the last decade of glass research is that a liquid, on cooling, approaches the glassy state non-uniformly. Some parts of the liquid become stiff while others retain the fluid mobility.

Harrowell, a pioneers of the study of these dynamic heterogeneities, likens them to ghostly echoes of the hidden secrets of the atomic disorder of the liquid.

“If we could understand what it is was in the arrangement of molecules that rendered one patch rigid and another liquid-like, we would be well on our way to being able to provide a complete account of the glass transition.”

However, there is one problem.

Nothing in the structural arrangements of model glasses studied using computer simulations seemed to be able to account for these huge variations in relaxation times. “Asaph and I had looked at everything - density, local structure, energy - nothing matched the spatial pattern of slow and fast particles. It had to be something more subtle.”

The breakthough came through a brief visit to David Reichman at Columbia University. “David was interested in looking at the vibrations in these model glasses. The results didn’t look very promising at first but, as we talked about it, we began to appreciate there were some real similarities between the pattern of slow vibrations and the pattern of mobile particles”, said Harrowell.

“Improvements in our understanding of this area have potential applications in the world of glassy films development, and could even provide future solutions to the current lifetime limitations of modern data storage devices,” said Harrowell.

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