Vasenkov Sergey, Schüring Andreas, Fritzsche Siegfried
Chemical Engineering Department, University of Florida, P.O. Box 116005, Gainesville, Florida 32611-6005, USA.
Langmuir. 2006 Jun 20;22(13):5728-33. doi: 10.1021/la060378w.
Molecular transport under the conditions of single-file diffusion was investigated near the channel boundaries by using dynamic Monte Carlo and molecular dynamics simulations of tracer exchange between single-file channels and their surroundings. The boundary effect reported in our recent papers (Vasenkov S.; Kärger, J. Phys. Rev. E 2002, 66, 052601. Schüring, A.; Vasenkov S.; Fritzsche, S. J. Phys. Chem. B 2005, 109, 16711) was studied in detail. This boundary effect is characterized by deviations of the intrachannel concentration profiles of tracer molecules observed in the case of single-file diffusion near the channel boundaries from the corresponding profiles typical for normal diffusion. It has been shown in our previous studies that these deviations occur under the conditions when the potential-energy difference inside and outside of single-file channels was both comparable and much larger than the activation energy of intrachannel diffusion. Here, we report a quantitative model describing the boundary effect. According to this model, an occurrence of the boundary effect is related to a complex character of diffusion in finite single-file systems. Such diffusion can be described by the following two types of movements occurring in parallel: (i) correlated displacements of all molecules in any particular channel and (ii) fast displacements of single molecules, which are uncorrelated with the displacements of all other molecules in the same channel. The latter displacements are restricted to a certain length interval that depends on the channel length and the channel occupancy. This length interval is shown to determine the extensions of the channel margins where the boundary effect is observed.
通过使用动态蒙特卡罗方法以及单通道与其周围环境之间示踪剂交换的分子动力学模拟，研究了单通道扩散条件下通道边界附近的分子输运。我们近期论文（Vasenkov S.；Kärger, J. Phys. Rev. E 2002, 66, 052601. Schüring, A.；Vasenkov S.；Fritzsche, S. J. Phys. Chem. B 2005, 109, 16711）中报道的边界效应得到了详细研究。这种边界效应的特征在于，在通道边界附近单通道扩散情况下观察到的示踪剂分子通道内浓度分布，与正常扩散典型的相应分布存在偏差。我们之前的研究表明，这些偏差发生在单通道内外势能差既可比又远大于通道内扩散活化能的条件下。在此，我们报告了一个描述边界效应的定量模型。根据该模型，边界效应的出现与有限单通道系统中扩散的复杂特性有关。这种扩散可以由以下两种并行发生的运动来描述：(i) 任何特定通道内所有分子的相关位移；(ii) 单个分子的快速位移，这些位移与同一通道内所有其他分子的位移不相关。后一种位移被限制在一定长度区间内，该区间取决于通道长度和通道占有率。结果表明，这个长度区间决定了观察到边界效应的通道边缘的范围。
