A charged colloidal particle suspended in an electrolyte experiences electroviscous stresses arising from motion-driven electrohydrodynamic phenomena. Under certain conditions, the additional contribution from electroviscous drag forces to the total drag experienced by the moving particle can lead to measurable deviations of particle diffusion coefficients from values predicted by the well known Stokes-Einstein relation that describes diffusive behavior of small particles in an unbounded charge-free fluid. In this study, we investigate the role of electroviscous stresses on nanoparticle diffusion in confined geometries using both simulations and experiment. We compare our experimental measurements with the results of a numerically solved continuum model based on the Poisson-Nernst-Planck-Stokes system of equations and find good agreement between experiment and theory. Depending on the radius of the counterion species in solution and the degree of confinement, we find that the viscous drag on polystyrene nanoparticles can be augmented by approximately 10–$25\%$ compared to the values predicted by pure hydrodynamic models in the absence of free charge in the fluid. This enhancement corresponds approximately to a 5–$10\%$ increase compared to the electroviscous contribution for a charged particle in an unbounded fluid. Contrary to recent reports in the experimental literature, we find neither experimental nor theoretical evidence of an anomalously large enhancement of electroviscous forces on a confined charged nanoparticle in solution.

中文翻译：

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溶液中受限纳米球的电粘效应

悬浮在电解质中的带电胶体颗粒会受到由运动驱动的电动流体现象产生的电粘应力。在某些条件下，电粘滞阻力对运动颗粒经历的总阻力的额外贡献可能导致颗粒扩散系数与由众所周知的斯托克斯-爱因斯坦关系预测的值可测量的偏差有关，该关系描述了无界小颗粒的扩散行为无电荷的流体。在这项研究中，我们使用模拟和实验方法研究电粘性应力对受限几何结构中纳米粒子扩散的作用。我们将实验测量结果与基于Poisson-Nernst-Planck-Stokes方程组的数值求解连续体模型的结果进行比较，发现实验与理论之间取得了良好的一致性。根据溶液中抗衡离子种类的半径和限制程度，我们发现聚苯乙烯纳米颗粒上的粘性阻力可以增加大约10–$25％$与在流体中不存在自由电荷的情况下，由纯流体力学模型预测的值进行比较。这种增强大约相当于5 –$10％$与无粘流体中带电粒子的电粘性贡献相比，该值增加了。与实验文献中的最新报告相反，我们没有发现实验性或理论性证据表明溶液中受限带电纳米粒子上的电粘滞力反常大幅度增加。