W0093

Structural Transitions Between Liquids and Glasses. J. Kieffer and R.E. Youngman, Department of Materials Science and Engineering, and J.D. Bass, Department of Geology, University of Illinois, Urbana, IL 61801

There is increasing evidence for the fact that glasses are inherently different from their melts, both structurally and thermodynamically. The results of Brillouin light scattering investigations of several glass-forming oxides will be presented. In these studies, the structural evolution with temperature were monitored by means of the high-frequency complex mechanical modulus. The storage modulus reflects the structural integrity and network connectivity, whereas the loss modulus represents the energy dissipated in aperiodic motions of small structural moieties. In order to describe the temperature dependence of the complex moduli consistently for all systems we investigated, we had to modify Maxwell's theory of visco-elasticity. Our model explicitly accounts for the transition between thermodynamically distinct structural states, one corresponding to the liquid, the other one to the glass. Using atomic-scale computer simulations, we were also able to identify underlying mechanisms of the transitions, and thereby uncover some attributes of the transforming structural states.

In addition, the application of our model to describe the temperature dependence of inherent structure energies obtained from molecular dynamic simulations of a binary Lennard-Jones fluid, will be presented as further support for the concept of structural distinction between liquids and glasses.