Laser-based measurement techniques for interfacial transport phenomena in microchannels

This paper summarized our recent works of the laser-based measurement techniques for investigating micro- and nano-scale transport phenomena. Micron-resolution particle image velocimetry combined with the laser induced fluorescence (LIF) technique was developed for analyzing velocity and ion concentration distributions simultaneously. The measurement system was based upon a confocal microscopy to realize the depth-resolution of approximately 2 μm, and this technique was applied to liquid-liquid mixing flows, gas-liquid two-phase flows and gas permeation phenomena through membranes. To evaluate the electrostatic potential at solid-liquid interface (i.e., zeta-potential), the LIF technique was advanced with the evanescent wave illumination. Fluorescent dye within approximately 100 nm from a microchannel wall was irradiated. This technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. Two proposed techniques will contribute to novel applications related to microscale multiphase flows or electrokinetics.