Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics (NLB2), The Ohio State University, Columbus, Ohio 43210-1142, United States.
Langmuir. 2013 Jun 11;29(23):6953-63. doi: 10.1021/la401168w. Epub 2013 May 28.
Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.
在微纳流体系中，减少流体阻力很重要。表面电荷和边界滑移会影响流体阻力，而且表面电荷也被认为会影响边界滑移。在固液界面上对表面电荷和边界滑移的定量研究已经很广泛，但对于表面电荷对边界滑移的影响还缺乏了解。在本文中，通过将表面电荷密度与静电力的理论模型相关联，拟合实验原子力显微镜（AFM）静电数据，定量了两种离子浓度的盐溶液和去离子（DI）水中浸泡的硼硅酸盐玻璃和十八烷基三氯硅烷（OTS）表面的表面电荷密度。结果表明，pH 值和电场会影响盐溶液和 DI 水中浸泡的玻璃和 OTS 表面的表面电荷密度。讨论了 pH 值和电场对表面电荷密度的影响机制。测量了两种离子浓度的盐溶液和不同 pH 值和电场的 DI 水中浸泡的 OTS 表面的滑移长度，并从表面电荷的角度分析了它们对滑移长度的影响。结果表明，OTS 表面的表面电荷密度绝对值越大，滑移长度越小。
