05. Micro- and Nano-Scale Transport, MEMS

There is a demand for improved performance in devices that utilize micro- and nano-scale channels, such as phase-change heat transfer devices and lab-on-a-chip systems. At such fine scales, the specific surface area is large, making it urgent to reduce frictional resistance, or in other words, to create a surface with significant fluid slip. While the existence of fluid slip was experimentally confirmed with the development of measurement technology in the latter half of the 20th century, the principle of fluid slip at solid-liquid interfaces has hardly been elucidated. One reason for this is the lack of experimental knowledge due to the low reliability of slip length measurement methods. In this study, we improved the analysis method for slip length measurement using an atomic force microscope (AFM). To compare the two methods that have been mainly used so far, the “intercept method” and the “recursive method,” we performed measurements on SiO2, graphite, and mica surfaces and compared the analysis results. We found that the spring constant of the AFM cantilever and fluid viscosity, which are calibrated in advance, contain large systematic errors in the existing methods, significantly affecting the calculation results of slip length. Therefore, we developed a new method, the “two-parameter method,” to solve these problems. In this method, the parameters that require prior calibration are consolidated into one fitting parameter, and fitting is performed using that parameter and the slip length as variables. This approach allows for deriving a more accurate and reliable slip length.