Enhanced Translational Diffusion and Spatially Heterogenous Dynamics in Supercooled Liquids

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Professor Mark Ediger of the Department of Chemistry of the University of Wisconsin-Madison is supported by a grant from the Theoretical and Computational Chemistry Program to perform experimental characterizations of the glass transition in supercooled organic liquids which include a number of polyaromatic compounds such as anthracene, tetracene4, rubrene and derivatives. Experiments are proposed to investigate the nature of molecular motion in deeply supercooled organic liquids to probe the nature of the liquid/glass transition. The questions that this research will address are: (1) What types of molecular motions occur in deeply supercooled liquids; (2) Is the supercooled liquid spatially heterogeneous; and (3) how is this connected to the non-exponential relaxation that is often observed. Optical, dielectric and NMR spectroscopies will be used to answer these questions, and in particular, how long-lived are the regions of different temperature, what is the connection between non-exponential dynamics and heterogeneity, what is the connection between heterogeneous dynamics and the observed enhancement of translation and if the anisotropic motion is the responsible for enhanced translation. In spite of the significant progress in the molecular interpretation of the static and dynamic properties of the liquid state, the properties of liquids and the molecular motions which occur near the glass transition temperature, are still not well understood. The experiments being conducted by Edgar are designed to shed light these problems, on the anomalous rotational and transactional relaxation, and the role of spatially inhomogeneous dynamics in the glass transition.