Visualization of Diffusion Phenomena in a Microchannel by using Near-infrared Light

Abstract

It is important and required for chemical analysis/synthesis using microfluidic channels to visualize diffusion phenomena and chemical reactions. We have thus developed a near-infrared (NIR) absorption imaging method to simultaneously measure the temperature and concentration distributions of aqueous solutions. This method is based on the fact that the ν₂ + ν₃ absorption band of water in an NIR region shifts to shorter wavelength as the temperature increases and that the band is very sensitive to the mole fraction of water. This paper shows the temperature and concentration images of aqueous solutions of methanol, ethanol, and glucose flowing in a Y-shaped microchannel. From the concentration images, the diffusion coefficient of each solute in water is determined by using a fitting function based on a one-dimensional diffusion equation, and its temperature dependence is quantitatively discussed.