Understanding the Properties of Supercooled Liquids and Glasses in Terms of Their Potential Energy Landscape

Orateur : Andreas HEUER (Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Münster, Germany)

Glass-forming systems display many fascinating properties such as the dramatic increase of relaxation time upon cooling or the presence of dynamic heterogeneities. Furthermore, upon strong external perturbations, as applied in microrheological or shear experiments, a characteristic response is observed. I start with a short review of some of these key features. Then I will introduce the concept of the potential energy landscape (PEL) which constitutes a general theoretical framework to capture many of these effects and to elucidate their underlying physical mechanisms. A few interesting applications will be discussed. First, it is shown how several dynamic equilibrium properties can be expressed in terms of the distribution of minima and barriers of the PEL as well as an elastic coupling between different regions of the supercooled liquid. Second, the thermodynamic as well as dynamic effects, observed for the microrheological perturbation, can be fully understood in terms of an effective temperature. This observation is a consequence of the statistical properties of the underlying PEL. The resulting scaling properties hold up to temperature significantly below the glass transition temperature. Third, the outcome of shear simulations for glasses can be related to the hopping dynamics in an appropriately defined PEL.

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