September 12, 2010

by Robin Donovan

Dr. Horacio Castillo, an Ohio University theoretical physicist, is currently completing work on the fourth year of a grant from the Department of Energy that has implications for our understanding of supercooled liquids, glasses, colloids and granular materials.

The initial grant was awarded for $254,987 in 2006. The project was later extended at no cost, then granted a one year $103,539 renewal in December 2009.

Castillo’s work seeks to characterize the glass transition that connects the liquid and the amorphous solid states. In a liquid, molecules move relatively quickly, but as temperature decreases, molecules move slower and liquids become more viscous. When a glass is formed, the molecules have essentially become frozen, caught in a disordered state, and the material is elastic, like a solid.

As the material transitions towards the glass state, Castillo said, “Not every part of this liquid is becoming slow in the same way, but actually if you manage to look at it microscopically, there are regions where the molecules are moving much slower than in other regions.”

Specifically, the funded study seeks to characterize how these inhomogeneous changes happen with numerical simulations and the creation of theories. Castillo’s research will further scientists’ understanding of viscosity, diffusivity and similar properties in supercooled liquids and glasses.

“We are doing a little bit of simulation and a little bit of theory and we are now starting to analyze experimental data, to see if this theory we’ve been developing is supported by the experiments,” said Castillo.

Castillo and his team at Ohio University have gathered experimental data from collaborators at Emory University, the University of Pennsylvania, and at Université Montpelier, France. They are also collaborating with groups at the University of Göttingen, Germany and at Bucknell University, who are working on simulations of granular materials. A renewal of the grant is in progress with the Department of Energy.