Hydrodynamic and entropic effects on colloidal diffusion in corrugated channels
Hydrodynamic and entropic effects on colloidal diffusion in corrugated channels
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DOI：
10.1073/pnas.1707815114
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发表时间：
2017-09-05
影响因子：
11.1
通讯作者：
Zhang, H. P.
中科院分区：
文献类型：
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作者：
Yang, Xiang;Liu, Chang;Zhang, H. P.
在没有平流的情况下，受限扩散表征了许多天然和人工装置（例如离子通道、沸石和纳米孔）中的传输。虽然关于这个问题的广泛的理论和数值研究已经产生了许多重要的预测，实验验证的预测是罕见的。在这里，我们实验测量胶体扩散时间在微通道周期性变化的宽度和对比结果与预测从菲克-雅各布斯理论和布朗动力学模拟。虽然理论和模拟正确地预测了不同通道宽度的熵效应，但它们未能考虑流体动力学效应，包括通道中扩散率的整体降低和空间变化。忽略这样的流体动力学效应，理论和模拟低估了40%的平均值和标准偏差的第一次通过时间的通道中的颈部宽度的颗粒直径的两倍。我们进一步表明，Fick-Jacobs理论的有效性，可以通过重新制定它的实验测得的扩散率。因此，我们的工作表明，流体动力学效应发挥了关键作用，通过狭窄的渠道扩散运输，并应包括在理论和数值模型。
In the absence of advection, confined diffusion characterizes transport in many natural and artificial devices, such as ionic channels, zeolites, and nanopores. While extensive theoretical and numerical studies on this subject have produced many important predictions, experimental verifications of the predictions are rare. Here, we experimentally measure colloidal diffusion times in microchannels with periodically varying width and contrast results with predictions from the Fick-Jacobs theory and Brownian dynamics simulation. While the theory and simulation correctly predict the entropic effect of the varying channel width, they fail to account for hydrodynamic effects, which include both an overall decrease and a spatial variation of diffusivity in channels. Neglecting such hydrodynamic effects, the theory and simulation underestimate the mean and standard deviation of first passage times by 40% in channels with a neck width twice the particle diameter. We further show that the validity of the Fick-Jacobs theory can be restored by reformulating it in terms of the experimentally measured diffusivity. Our work thus shows that hydrodynamic effects play a key role in diffusive transport through narrow channels and should be included in theoretical and numerical models.