Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Soft Matter. 2019 Feb 13;15(7):1582-1596. doi: 10.1039/c8sm01360h.
The accurate measurement of wall zeta potentials and solute-surface interaction length scales for electrolyte and non-electrolyte solutes, respectively, is critical to the design of many biomedical and microfluidic applications. We present a novel microfluidic approach using diffusioosmosis for measuring either the zeta potentials or the characteristic interaction length scales for surfaces exposed to, respectively, electrolyte or non-electrolyte solutes. When flows containing different solute concentrations merge in a junction, local solute concentration gradients can drive diffusioosmotic flow due to electrokinetic, steric, and other interactions between the solute molecules and solid surfaces. We demonstrate a microfluidic system consisting of a long, narrow pore connecting two large side channels in which solute concentration gradients drive diffusioosmosis within the pore, resulting in predictable fluid velocity/pressure and solute profiles. Furthermore, we present analytical results and a methodology to determine the zeta potential or interaction length scale for the pore surfaces based on the solute concentrations in the main side channels, the flow rate in the pore, and the pressure drop across the pore. We apply this method to the experimental data of Lee et al. to predict the zeta potentials of their system, and we use 3D numerical simulations to validate the theory and show that end effects caused by the junctions are negligible for a wide range of parameters. Because the dynamics in the proposed system are driven by diffusioosmosis, this technique does not suffer from certain disadvantages associated with the use of sensitive electronics in traditional zeta potential measurement approaches such as streaming potential, streaming current, or electroosmosis. To the best of our knowledge this is the first flow-based approach to characterize surface/solute interactions with non-electrolyte solutes.
准确测量壁面 ζ 电位和电解质与非电解质溶质的固-液相互作用长度尺度，对于许多生物医学和微流控应用的设计至关重要。我们提出了一种新颖的基于扩散渗流的微流控方法，用于测量暴露于电解质或非电解质溶质的表面的 ζ 电位或特征相互作用长度尺度。当含有不同溶质浓度的流体在连接处合并时，由于溶质分子与固体表面之间的电动、空间位阻和其他相互作用，局部溶质浓度梯度可以驱动扩散渗流。我们展示了一种由连接两个大侧通道的长而窄的孔组成的微流控系统，其中溶质浓度梯度在孔内驱动扩散渗流，导致可预测的流体速度/压力和溶质分布。此外，我们提出了一种基于主侧通道中的溶质浓度、孔内流速和孔压降来确定孔表面 ζ 电位或相互作用长度尺度的分析结果和方法。我们将该方法应用于 Lee 等人的实验数据，以预测他们系统的 ζ 电位，并使用 3D 数值模拟验证理论并表明，由于接头引起的末端效应在广泛的参数范围内可以忽略不计。由于所提出系统中的动力学是由扩散渗流驱动的，因此该技术不会遭受与传统 ζ 电位测量方法（如流动电势、流动电流或电渗流）中使用灵敏电子相关的某些缺点。据我们所知，这是首次基于流动的方法来表征非电解质溶质与表面的相互作用。
