Abstract：
Fluid drag of micro/nano fluidic systems has inspired wide scientific interest. Surface charge and boundary slip at the solid-liquid interface are believed to affect fluid drag. This review summarizes the recent studies on the coupling of surface charge and slip, and their combined effect on fluid drag at micro/nano scale. The effect of pH on surface charge of borosilicate glass and silica surfaces in deionized (DI) water and saline solution is discussed using a method based on colloidal probe atomic force microscopy (AFM). The boundary slip of various oil-solid interfaces are discussed for samples with different degrees of oleophobicity prepared by nanoparticle-binder system. By changing the pH of solution or applying an electric field, effect of surface charge on slip of a smooth hydrophobic octadecyltrichlorosilane (OTS) in DI water and saline solution is studied. A theoretical model incorporating the coupling relationship between surface charge and slip is used to discuss the combined effect of surface charge-induced electric double layer (EDL) and slip on fluid drag of pressure-driven flow in a one-dimensional parallel-plates microchannel. A theoretical method is used to reduce the fluid drag. The studies show that the increasing magnitude of surface charge density leads to a decrease in slip length. The surface charge results in a larger fluid drag, and the coupling of surface charge and slip can further increase the fluid drag. Surface charge-induced EDLs with asymmetric zeta potentials can effectively reduce the fluid drag.
摘要：
微/纳米流体系统的流体阻力激发了广泛的科学兴趣。固液界面处的表面电荷和边界滑移被认为会影响流体阻力。本文综述了表面电荷与滑移耦合的最新研究，以及它们在微/纳米尺度上对流体阻力的综合影响。使用基于胶体探针原子力显微镜（AFM）的方法讨论了pH对去离子（DI）水和盐溶液中硼硅酸盐玻璃和二氧化硅表面表面电荷的影响。对于由纳米颗粒-粘合剂体系制备的具有不同疏油性程度的样品，讨论了各种油固界面的边界滑移。通过改变溶液的pH值或施加电场，研究了表面电荷对光滑疏水十八烷基三氯硅烷（OTS）在DI水和盐溶液中滑移的影响。结合表面电荷与滑移之间耦合关系的理论模型用于讨论表面电荷感应双电层（EDL）和滑移对一维平行板微通道中压力驱动流的流体阻力的综合影响。采用理论方法减小流体阻力。研究表明，表面电荷密度的增加导致滑动长度的减少。表面电荷导致更大的流体阻力，表面电荷和滑移的耦合可以进一步增加流体阻力。表面电荷诱导的具有非对称ζ电位的EDL可以有效地降低流体阻力。
