Evaluation of passive mixing behaviors in a pillar obstruction poly(dimethylsiloxane) microfluidic mixer using fluorescence microscopy

The rapid mixing of fluids passing through a microfluidic channel is very important for various applications of microfluidic systems. It has been a great challenge to achieve highly efficient mixing in a microfluidic system because it is very difficult to generate turbulence in a submillimeter-size channel at low Reynolds numbers (Re). In this paper, we fabricated a pillar obstruction microfluidic mixer and evaluated its mixing efficiency at various flow rates. The mixing behavior of confluent streams was estimated using a fluorescence microscope. Three different sets of miscible solutions (phosphate-buffered solution, gold nanocolloids and 20% glycerol), with Rhodamine 6G aqueous solution, were used as sample laminar flows. According to our experimental results, the pillar obstruction microfluidic mixer shows an excellent mixing performance in the low Re range. Here, the mixing performance was strongly dependent on the characteristic viscosity changes of different sets of miscible solutions. The pillar obstruction microfluidic mixer designed here is expected to benefit a wide range of lab-on-a-chip applications because fabrication is very simple and the mixing efficiency is excellent at low Re.