Direct Observation of Dispersion and Mixing Processes in Microfluidic Systems

Abstract

The diffusion phenomena, dispersion and mixing processes of the sample solute (Basic Blue 3 dye and KMnO₄ aqueous solutions) were directly observed in laminar flow in glass microchannels. Quasi steady-state UV-visible absorption spectrometry was carried out using CCD camera images of the colored sample dispersion and mixing processes, and the absorbance change (ΔAbs) was discussed based on the dimensionless parameter, τ which represents the flow time renormalized to the diffusion coefficient and the channel cross section. It was found that ΔAbs showed almost the same τ dependence, even though the solutions and the microchannel sizes differed in laminar flow, if the microchannel fabrication method was the same. On the basis of this fundamental result, the total microchannel length required for the reaction of 2,3-diaminonaphthalene (DAN) and NO₂^- at a flow rate of 2 µL min^-1 was calculated, and the obtained value (∼100 mm) showed very good agreement with our previous microchip research. It was concluded that both results were useful for designing the microchannel width, depth and length to control the chemical reaction time in recent microfluidic systems.