Simultaneous Nanoscale-Resolution Measurement of Fluid Slip and Charge at Solid-Liquid Interfaces

The fluid slip at solid–liquid interfaces can significantly affect fluid flow in micro- and nanochannels. The magnitude of the slip can be influenced by nanoscale roughness and surface charge; however, its extent remains unclear due to the limited spatial resolution of conventional measurement techniques. Although techniques such as particle image velocimetry, surface force apparatus, and nanochannel flow measurements have been used to measure slip length, they are either limited to transparent samples or lack sufficient resolution to probe nanoscale surface characteristics. To address these limitations, we developed a novel technique based on frequency-modulation atomic force microscopy, which enables mapping of fluid slip with over 20 times greater spatial resolution than conventional methods. This approach was successfully applied to a variety of solid surfaces including SiO₂, DLC, HOPG, Teflon, and mica, under both pure water and KCl solutions of varying concentrations. As a result, we achieved simultaneous nanoscale visualization of slip length, surface topography, and interfacial charge distribution. This technique holds strong potential for deepening our understanding of interfacial fluid dynamics and wetting phenomena.