Combined laser-based measurements for micro-and nanoscale transport phenomena

The present paper summarizes our recent research in combined laser-based measurement techniques for investigating micro-and nanoscale transport phenomena. Micrometer-resolution particle image velocimetry has been combined with the laser-induced fluorescence (LIF) technique in order to simultaneously analyze velocity and scalar fields. The measurement system is based on confocal microscopy to realize a depth resolution of approximately 2 m, and we have applied this technique to liquid-liquid mixing flows, gas-liquid two-phase flows, gas permeation phenomena through membranes, and surface-modified microchannel flow. Furthermore, in order to evaluate the electrostatic potential at a solid-liquid interface (i.e., zeta potential), the LIF technique was extended by evanescent wave illumination, and only the fluorescent dye within approximately 100 nm of the microchannel wall was irradiated. The extended LIF technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. The proposed techniques will contribute to novel applications related to microscale multiphase flows or electrokinetics.