Study of droplet coalescence in micro-channels

This project focuses on the study of the reliable merging of plugs at the junction using 200µm (width) by 100µm (height) PDMS micro-channels. The micro-channels are fabricated using soft lithography. The carrier phase used is mineral oil (Sigma M5904) with 2% w/w Span 80 surfactant (Sigma s6760). The dispersed phase is DI water with 0.05% w/w Acid Yellow 73 florescence dye (Sigma F6377). The reagent used in the experiments is DI water. The Nikon inverted microscope is used in conjunction with other imaging equipments to capture the flow videos and images for the analysis. Many groups have studied the process of merging using the simple T-junction. However, the merging region is confined to limited flow rate combinations. In order to expand the region of reliable merging, the author has come up with two designs that incorporate expansion bracket 50µm downstream of the T-junction. Results have shown that the addition of the expansion bracket would aid in expanding the reliable merging region. It would also facilitate the mixing time in plugs. Serpentine section has been added after the junction to reduce the time needed for mixing. The radius of the serpentine section is 1000µm. It is also found that changes in the DI water substrate flow rate would alter the amount of reagent being injected into the plugs. Analysis on the plugs formation at the upstream Y-junction has also been carried out to understand the merging process better. Results have shown that a higher carrier fluid flow rate would result in smaller plugs and longer distance between plugs. This would impede the reliable merging process and it is not desirable. Contaminations of the DI water substrate and contamination of successive florescence plugs are also observed in the experiments.Bachelor of Engineering (Mechanical Engineering