Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL, United States.
J Colloid Interface Sci. 2011 Jul 15;359(2):520-9. doi: 10.1016/j.jcis.2011.03.088. Epub 2011 Apr 2.
The electrokinetic behavior of nanofluidic devices is dominated by the electrical double layers at the device walls. Therefore, accurate, predictive models of double layers are essential for device design and optimization. In this paper, we demonstrate that density functional theory (DFT) of electrolytes is an accurate and computationally efficient method for computing finite ion size effects and the resulting ion-ion correlations that are neglected in classical double layer theories such as Poisson-Boltzmann. Because DFT is derived from liquid-theory thermodynamic principles, it is ideal for nanofluidic systems with small spatial dimensions, high surface charge densities, high ion concentrations, and/or large ions. Ion-ion correlations are expected to be important in these regimes, leading to nonlinear phenomena such as charge inversion, wherein more counterions adsorb at the wall than is necessary to neutralize its surface charge, leading to a second layer of co-ions. We show that DFT, unlike other theories that do not include ion-ion correlations, can predict charge inversion and other nonlinear phenomena that lead to qualitatively different current densities and ion velocities for both pressure-driven and electro-osmotic flows. We therefore propose that DFT can be a valuable modeling and design tool for nanofluidic devices as they become smaller and more highly charged.
纳米流体设备的电动行为主要由设备壁处的双电层决定。因此，对于设备设计和优化，准确、可预测的双电层模型是必不可少的。在本文中，我们证明了电解质的密度泛函理论（DFT）是一种计算有限离子尺寸效应和经典双电层理论（如泊松-玻尔兹曼）忽略的离子-离子相关的准确且计算效率高的方法。由于 DFT 是从液体理论热力学原理推导出来的，因此它非常适合具有小空间尺寸、高表面电荷密度、高离子浓度和/或大离子的纳米流体系统。在这些情况下，离子-离子相关预计会很重要，导致非线性现象，如电荷反转，其中更多的抗衡离子吸附在壁上，超过中和其表面电荷所需的数量，导致第二层共离子。我们表明，与不包括离子-离子相关的其他理论不同，DFT 可以预测电荷反转和其他非线性现象，这些现象导致压力驱动和电渗流的电流密度和离子速度发生定性变化。因此，我们提出 DFT 可以成为纳米流体设备的有价值的建模和设计工具，因为它们变得更小且带电量更高。
