Concentration-adjustable micromixers using droplet injection into a microchannel.

A novel micromixing technique that exploits a thrust of droplets into the mixing interface is developed. The technique enhances the mixing by injecting immiscible droplets into a mixing channel and the methodology enables control of the mixing level simply by changing the droplet injection frequency. We experimentally characterize the mixing performance with various droplet injection frequencies, channel geometries, and diffusion coefficients. Consequently, it is revealed that the mixing level increases with the injection frequency, the droplet-diameter-to-channel-width ratio, and the diffusion coefficient. Moreover, the mixing level is found to be a linear function of the droplet volume fraction in the mixing section. The results suggest that the developed device can produce a large amount of sample solution whose concentration is arbitrary and precisely controllable with a simple and stable operation.