Estimation of surface slippage in nanogap based on flow velocity distributions obtained by nanoparticle image velocimetry

Abstract

With the development of microfabrication and surface treatment technologies, the gaps between elements in mechanical and electronic components have narrowed from the micrometer to the nanometer-sized. Fluid slippage at the solid/liquid interface is one of the phenomena that are considered to occur in micro/nanometer-sized gaps, and frictional properties there are expected to be different from those in macro gaps. For proper lubrication design in nanometer-sized gap, it is necessary to quantify the slippage at the interface. In this study, we used the fluorescence tracking of quantum dots with diameters of a few nanometers to measure the squeezed flow in nanometer-sized gap. Quantitative lateral velocity distributions were measured, and we estimated the slippage based on our proposed analysis of the number distribution of measured velocity values that depends on the flow profile in the depth direction. Our obtained results suggested that interfacial slippage occurred in the gap about less than 200 nm.