Mixing characterization inside micro - droplets engineered on a

We use a micro-device where micro-droplets of reagents are generated and coalesce in a carrier continuous phase. The work focuses on the characterization of the mixing step inside the droplets, in the perspective to use them for chemical kinetic data acquisition. A dye and water are used, and an acid-base instantaneous chemical reaction is monitored thanks to a colored indicator. Acquisitions are done with a high speed camera coupled to a microscope and a mixing parameter is calculated by image analysis. Different angles of bended channels and different ways of coalescence are compared. It is shown that the homogenization of the droplets can be reached in less than ten milliseconds after coalescence. This is achieved by forcing the droplets to coalesce in a “shifted” way, and later by adding 45 degrees angle bends along the channel.