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A free-energy landscape picture and Landau theory for the dynamics of disordered materials

Mohammad Reza H. Javaheri·Ralph V. Chamberlin
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Abstract

Landau's theory of phase transitions is adapted to treat independently relaxing regions in complex systems using nanothermodynamics. The order parameter we use governs the thermal fluctuations, not a specific static structure. We find that the entropy term dominates the thermal behavior, as is reasonable for disordered systems. Consequently, the thermal equilibrium occurs at the internal-energy maximum, so that the minima in a potential-energy landscape have negligible influence on the dynamics. Instead the dynamics involves normal thermal fluctuations about the free-energy minimum, with a time scale that is governed by the internal-energy maximum. The temperature dependence of the fluctuations yields VTF-like relaxation rates and approximate time-temperature superposition, consistent with the WLF procedure for analyzing the dynamics of complex fluids; while the size dependence of the fluctuations provides an explanation for the distribution of relaxation times and heterogeneity that are found in glass-forming liquids, thus providing a unified picture for several features in the dynamics of disordered materials.

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Mohammad Reza H. Javaheri, Ralph V. Chamberlin. 2006-12-05. A free-energy landscape picture and Landau theory for the dynamics of disordered materials. https://doi.org/10.1063/1.2354471

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