咪唑离子液体中输运系数的分子动力学研究

近些年来，离子液体由于其独特的性能，如高的热稳定性、低的蒸气压和良好的导电性能等，而在材料应用和基础研究上受到广泛的关注。离子液体的这些特性都和其液体的输运系数，如粘度、扩散系数和电导率密切相关。当温度降低时，这些输运系数出现了一些异常现象，如非Arrhenius的转变和Stokes-Einstein（SE）关系的失效等。输运系数的这些异常行为给离子液体的应用和理论带来了严峻的挑战。本项目以常用的咪唑离子液体作为研究对象，在改变碳链长度的情况下研究旋转动力学对这些输运系数的影响，以及它与平移动力学的耦合和退耦合关系。项目的创新性在于提出了离子液体中旋转自由度的弛豫对液体宏观输运系数具有重要的影响，而不仅仅只有传统的简单液体中所被广泛接受的平移弛豫过程，如笼子效应和动力学不均匀性。

Recently, ionic liquids (ILs) are attracting tremendous interests both in functional application and fundamental researches, due to their unique liquid properties, such as nonvitality, low vapor pressure, and high conductivity. All these unique properties are intimately correlated with their transport coefficients, i.e., the shear viscosity, diffusion coefficient, and electric conductivity. Upon cooling down, many anomalous phenomena happen for the transport coefficient, e.g., the non-Arrhenius transition and breakdown of Stokes-Einstein (SE) relation. These abnormal phenomena set difficulty for the application of these materials and challenge theories of them. In this project, we utilize the imidazolium-based ionic liquids as a prototype of ILs, to investigate the influence of rotational dynamics on the transport processes with the variation of alkyl-chain length, as well as the coupling and decoupling of it with translational dynamics. Innovation of the project comes from the proposal that rotational dynamics plays a significant role on the macroscopic transport processes, which is in contrast to the traditional concept that is widely accepted in simple liquid such as cage effect and dynamic heterogeneity.