固液界面的表面电荷会影响微纳流体系统的流体阻力, 因此如何测量固液界面的表面电荷密度以及分析表面电荷的产生机理对于研究表面电荷对流体阻力的影响具有较大的意义。提出了一种基于接触式AFM的固液界面表面电荷密度测量方法。基于该方法测量了浸在去离子水和0.01 mol/L的NaCl溶液中的高硼硅玻璃和二氧化硅样本的表面电荷密度, 并研究了溶液pH值对表面电荷的影响。研究结果表明高硼硅玻璃和二氧化硅由于表面硅烷基的电离带负电。溶液pH值和离子浓度的增加都会增加浸在去离子水和0.01 mol/L的NaCl溶液中高硼硅玻璃和二氧化硅的表面电荷密度的绝对值。

Fluid drag in the micro/nano fluidics is an object of scientific interest and surface charge at the solid-liquid interfaces is believed to affect fluid drag. How to measure the surface charge density and analyze the origin of surface charge at the solid-liquid interfaces are significant. Because the electrostatic force is related to the surface charge density and colloidal probe AFM can measure the electrostatic force with nanoscale resolution, a theoretical model between the electrostatic force applied on the AFM colloidal probe and the surface charge density at the solid-liquid interface is first developed and a method based on AFM is developed. Then the newly developed method is used to measure the surface charge densities of borosilicate glass and silica surfaces immersed in deionized (DI) water and 0.01 mol/L saline solution with pH value range from 3 to 10. The results show that borosilicate glass and silica surfaces in DI water and 0.01 mol/L saline solution are negatively charged because of the dissociation of silanol groups. Both the increasing pH value and ionic concentration can result in the increasing surface charge density of borosilicate glass and silica surface immersed in DI water and 0.01 mol/L saline solution. Furthermore, the colloidal probe AFM method is a useful technique to measure the surface charge density with high resolution.