Enhanced Translational Diffusion and Spatially Heterogenous Dynamics in Supercooled Liquids

威斯康星大学麦迪逊分校化学系的Mark Ediger教授得到了理论和计算化学计划的资助，负责对过冷有机液体中的玻璃化转变进行实验表征，这些过冷有机液体包括许多多芳香族化合物，如菲、四烯4、Rubrene及其衍生物。通过实验研究了深过冷有机液体中分子运动的本质，以探索液体/玻璃转变的本质。这项研究将解决的问题是：(1)在深过冷液体中发生什么类型的分子运动；(2)过冷液体在空间上是不均匀的；(3)这与经常观察到的非指数弛豫有何联系。光学、介电和核磁共振光谱将被用来回答这些问题，特别是不同温度区域的寿命有多长，非指数动力学和非均质性之间有什么联系，非指数动力学和观察到的平移增强之间有什么联系，以及各向异性运动是否对平移增强负责。尽管在液体的静态和动态性质的分子解释方面取得了重大进展，但液体的性质以及在玻璃化转变温度附近发生的分子运动仍然不被很好地理解。埃德加正在进行的实验旨在阐明这些问题，包括反常的转动和相对论弛豫，以及空间不均匀动力学在玻璃化转变中的作用。

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.