School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
J Phys Chem B. 2011 Oct 13;115(40):11700-11. doi: 10.1021/jp206811a. Epub 2011 Sep 21.
The recent frictional model of the transport of fluid mixtures in nanopores developed in this laboratory is extended here to formulate a new theory of the self-diffusion of Lennard-Jones fluids in cylindrical pores by considering the problem of diffusion of identical molecules that differ only in color. The new theory is found to predict the self-diffusivity accurately over a wide range of densities and pore sizes, extending from molecularly narrow pores to large mesopores. However, deviations from the theory appear near to the critical temperature where the correlation length of the fluid diverges and when intermolecular interactions are important in molecularly narrow pores. Under such circumstances, local averaging of the fluid-fluid density to obtain a local viscosity does not adequately capture the effects of viscous friction. A new criterion is developed for determining the significance of fluid-fluid intermolecular interactions in a nanopore by considering the ratio of oscillation times of a fluid molecule in the force field of the surrounding fluid molecules and that in the force field of the pore wall. The ratio is shown to give good predictions of the region where intermolecular interactions are important and explains the region of deviation between theory and simulation in molecularly narrow pores.
本实验室最近开发的用于纳米孔中混合流体输运的摩擦模型在此基础上进行扩展，通过考虑仅在颜色上有所不同的相同分子的扩散问题，提出了一种新的圆柱形孔中 Lennard-Jones 流体自扩散理论。该新理论在很宽的密度和孔径范围内准确预测了自扩散系数，涵盖了从分子狭窄孔到较大介孔的范围。然而，在接近流体相关长度发散的临界温度以及在分子狭窄孔中分子间相互作用很重要的情况下，该理论会出现偏差。在这种情况下，通过对流体-流体密度进行局部平均以获得局部粘度，并不能充分捕捉粘性摩擦的影响。通过考虑流体分子在周围流体分子的力场中和在孔壁的力场中的振动时间之比，提出了一种新的准则来确定纳米孔中流体-流体分子间相互作用的重要性。该比值很好地预测了分子间相互作用重要的区域，并解释了分子狭窄孔中理论与模拟之间的偏差区域。
