Diffusioosmosis-driven dispersion of colloids: a Taylor dispersion analysis with experimental validation
Diffusioosmosis-driven dispersion of colloids: a Taylor dispersion analysis with experimental validation
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DOI：
10.1017/jfm.2022.321
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发表时间：
2022-05-24
影响因子：
3.7
通讯作者：
Stone, Howard A.
中科院分区：
文献类型：
--
作者：
Alessio, Benjamin M.;Shim, Suin;Stone, Howard A.
扩散电泳是指胶体颗粒在溶质浓度梯度存在下的运动，并且使得胶体颗粒能够在不可接近的几何形状（例如死端孔）中定向运动，而不施加外部场。以前的实验报告死端孔的几何形状表明，即使在平均流量的情况下，通过扩散电泳移动的胶体颗粒表现出显着的分散。现有的扩散电泳模型不能预测分散，因此实验和模型之间的比较主要是定性的。为了解决这些定量的实验和模型之间的差异，我们推导出一个有效的一维方程，类似于泰勒色散分析，占从通道侧壁的扩散渗透流创建的色散。我们推导出有效的色散系数，并通过与直接数值模拟进行比较来验证我们的结果。我们还比较了我们的模型与实验，并获得了广泛的胶体颗粒尺寸的定量协议。我们的分析揭示了两个重要结论。首先，在不存在平均流的情况下，分散由扩散渗透壁滑移产生的流动驱动，使得可以通过降低通道壁扩散渗透流动性来减少扩散。第二，该模型可以解释胶体在死端孔中的扩散，适用于各种粒径。我们注意到，虽然这里提出的分析集中在一个死端孔的几何形状，没有平均流量，我们的理论框架是通用的，可以适应其他几何形状和其他背景流。
Diffusiophoresis refers to the movement of colloidal particles in the presence of a concentration gradient of a solute and enables directed motion of colloidal particles in geometries that are inaccessible, such as dead-end pores, without imposing an external field. Previous experimental reports on dead-end pore geometries show that, even in the absence of mean flow, colloidal particles moving through diffusiophoresis exhibit significant dispersion. Existing models of diffusiophoresis are not able to predict the dispersion and thus the comparison between the experiments and the models is largely qualitative. To address these quantitative differences between the experiments and models, we derive an effective one-dimensional equation, similar to a Taylor dispersion analysis, that accounts for the dispersion created by diffusioosmotic flow from the channel sidewalls. We derive the effective dispersion coefficient and validate our results by comparing them with direct numerical simulations. We also compare our model with experiments and obtain quantitative agreement for a wide range of colloidal particle sizes. Our analysis reveals two important conclusions. First, in the absence of mean flow, dispersion is driven by the flow created by diffusioosmotic wall slip such that spreading can be reduced by decreasing the channel wall diffusioosmotic mobility. Second, the model can explain the spreading of colloids in a dead-end pore for a wide range of particle sizes. We note that, while the analysis presented here focuses on a dead-end pore geometry with no mean flow, our theoretical framework is general and can be adapted to other geometries and other background flows.