When 9:00 AM - 10:30 AM Oct 27, 2006
Where 1670 CSE
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Dynamics and Thermodynamics of the Glass Transition

James Langer, University of California – Santa Barbara

One of the most fascinating mysteries in statistical physics is the nature of the glass transition. What mechanism causes, for example, the viscosities of glass forming fluids to diverge at finite temperatures? And what is the connection between this dynamic behavior and the remarkable thermodynamic properties of these materials?

The principal theme of this talk is that these anomalously slow, super-Arrhenius relaxation processes may be activated by chains of atomic displacements. Such chains are seen in molecular-dynamics simulations, for examle, those of Glotzer and coworkers. The entropy of sufficiently long excitation chains can enable them to grow without bound, thus nucleating long-lasting fluctuations in the density or atomic coordination. I argue that the intrinsic atomic-scale disorder in a glass plays an essential role in determining the activation rate for such chains, and show that the resulting rate formula is essentially the same as the Vogel-Fulcher law. A key feature of this theory is that the spatial extent of critically long excitation chains diverges at the Vogel-Fulcher temperature. I speculate how this diverging length scale may explain the vanishing configurational entropy and other observed relations between dynamics and thermodynamics at the glass transition.

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