Combined laser-based measurements for micro- and nano-scale transport phenomena

Abstract

This paper summarizes our recent works in combined 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 has been developed for analyzing velocity and ion concentration distributions simultaneously. The measurement system was based upon a confocal microscope to realize the depth-resolution of approximately 2 μm, and we have applied this technique to liquid-liquid mixing flows, gas-liquid two-phase flows and gas permeation phenomena through membranes. To evaluate the electrostatic potential at a solid-liquid interface (i.e., zeta-potential), the LIF technique was extended with evanescent wave illumination, and only the fluorescent dye within approximately 100 nm from a microchannel wall was irradiated. The technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. Two proposed developments will contribute to novel applications related to microscale multiphase flows or electrokinetics.