Effect of channel geometry on alternating droplet generation

Abstract

Droplet based micro uidics has been one of the popular topics in micro udics research for the past two decades due to several advantages which include: less amount of reagent (sample) being used, enhanced mixing in the drops due to chaotic advection, low thermal mass and large surface to volume ratio which results in e cient heat transfer and encapsulation of reagents in droplets. Producing droplets from two sources inside the same micro-channel has been attempted by several research groups with great success and it carries great signi cance due to its applications in chemical synthesis, biological analysis and targeted drug delivery. While there are geometries available to produce synchronized alternating droplets, the mechanism of alternation in such device has not been studied. In this work a cross junction device (also known as a double T-junction device)is used; and the e ect of the taper angle of the side inlet channels on the continuous generation of an alternating pattern is studied. It was found that a higher value of the taper angle results in more e cient and constantly repeating alternating pattern of droplets from the two sources. This study includes the statistical analysis of the experimental data to compare the performance of devices with di erent taper angles for side channels. Moreover the experimental data is used to measure the radii of curvature at the instant of break o and used to calculate the Laplace pressure drop across the junction which enables us to compare the total pressure drop across the junction for devices with di erent taper angle values. Using the total pressure drop it was concluded that the hydraulic resistance of the side inlet channels is the key factor in synchronized alternating droplet pattern generation. In order to con rm the calculated values, a computational study is also performed which further substantiates the theory. Furthermore, using the tapered channel devices, di erent patterns are generated that are referred to as barcodes, by employing di erent ow rate combinations at the dispersed phase inlets. Finally it was showed how to generate barcodes composed of droplets with di erent and same viscosity. The signi cance of being able to generate di erent patterns is related to being able to separately identify droplets from each sources while using automation in the system since the droplet size and spacing remains uniform.