离子液体自由体积的分子动力学模拟

The correlation between macroscopic physical properties and microscopic structural is a fundamental topic in material science. Free volume that exists due to static and dynamic disorder of the structure influences the substance properties such as mass density, viscosity, structure relaxation, physical aging, phase transition, conductivity, mobility, permeability etc. Free volume theory is applied extensively in the field of glass transition and physical properties in polymer material. Nevertheless, it is not the case for the ionic liquids. The most extensively and successfully applied technique for determining the distribution of local free volume is the positron annihilation lifetime spectroscopy (PALS).But there are limitation for the experiment, the molecular dynamics simulation doesn’t have the flaw of experiment, meanwhile, it could represent free volume structure in microscopic scale, explain the influence of free volume to the molecular diffusion and transport property, it could also give the information of force between particles and energy. This work will apply the molecular dynamics simulation to obtain the information of free volume parameters in ionic liquids, compare the result with the data from positron lifetime spectroscopy, and then apply to other ionic liquids, establish the correlation between microscopic scale free volume structure and macroscopic transport property, implement “bottom-up” molecular design of ionic liquids.

宏观物理性质与微观结构之间的关系是材料科学的重要研究课题.由于分子的静态与动态无规所产生的自由体积(孔洞)对于物质的宏观性质,如密度,粘滞性,结构弛豫,物理老化,相变,电导性,流动性,渗透性等都有很重要的影响。孔洞理论在高聚物材料的玻璃态转变及其物性研究中已经得到了广泛的应用，但在离子液体材料中还少有相关工作。研究孔洞体积的实验方法中最有效的方法为正电子寿命谱实验,但是正电子寿命谱具有自身实验方法的局限性,而分子动力学模拟方法可以弥补正电子实验方法的限制，并可以在微观尺度上获得自由体积结构,解释孔洞体积对分子扩散，输运性质的影响,同时也可得到分子间力与能量信息。本工作将致力于利用分子动力学模拟方法获得离子液体孔洞体积参数信息，与已有正电子寿命谱实验结果相比较,并应用于其它离子液体中,建立离子液体微观孔洞结构和宏观输运性质的关系，实现离子液体“自下而上”的分子设计。