Ghorai Pradip Kr, Yashonath S, Lynden-Bell R M
Solid State and Structural Chemistry Unit and Center for Condensed Matter Theory, Indian Institute of Science, Bangalore, India 560 012.
J Phys Chem B. 2005 Apr 28;109(16):8120-4. doi: 10.1021/jp044605j.
We propose an alternative explanation of the size-dependent maximum in ion mobility in water in terms of the levitation effect, which accounts for the observed size-dependent maximum in the mobility of guest diffusion in porous media. In this explanation, the size at which the maximum occurs is related to the structure of the void space of the water; at the mobility maximum, the diffusant passes smoothly through necks connecting voids, and its potential energy shows minimum fluctuations. Molecular dynamics simulations of charged spheres of varying sizes are used to support this hypothesis. As in the levitation effect, the friction coefficient, the potential energy fluctuations, and the activation energy are found to be minima for particles with maximum self diffusivities similar to the guest diffusion in zeolites. Wavelength-dependent self diffusivities indicate a monotonic and oscillatory dependence, respectively, on wavenumber k for anomalous (AR) and linear regimes (LR). These are associated with single and biexponential decay of the incoherent intermediate scattering function.
我们根据悬浮效应提出了一种关于水中离子迁移率与尺寸相关的最大值的替代解释，该效应解释了在多孔介质中客体扩散迁移率中观察到的与尺寸相关的最大值。在此解释中，出现最大值的尺寸与水的空隙空间结构有关；在迁移率最大值处，扩散剂顺利通过连接空隙的颈部，其势能波动最小。使用不同尺寸带电球体的分子动力学模拟来支持这一假设。与悬浮效应一样，发现对于具有最大自扩散率的粒子，摩擦系数、势能波动和活化能最小，类似于沸石中的客体扩散。波长依赖性自扩散率分别表明反常（AR）和线性区域（LR）对波数k的单调和振荡依赖性。这些与非相干中间散射函数的单指数和双指数衰减相关。
