Influence of Microfluidic Geometry on Micro-droplet Formation

Microfluidic technologies open the door to a multitude of novel applications in biological and chemical analytics. Microfluidic environments provide highly controllable and reproducible laminar flows. Aqueous micro-droplets can be formed using a characteristic cross-junction microstructure called a flow focusing element where the oil (continuous) phase surrounds and breaks off aqueous droplets (dispersed phase). This technology could be used encapsulate a controlled amount of reagent within the micro-droplets. This fabrication process may introduce slight geometric differences from device to device due to manufacturing tolerances and non-uniformity in fabrication steps by the operator. These deviations can influence the formation of droplets within the device by creating slightly altered velocity profiles which affect the genesis of the drop itself. The purpose of this work was to study the generation of micro-droplets in six slightly varying device geometries to better understand the effect of flow patterns on the formation of monodisperse droplets. The rounding of the corners of the cross-junction was 0, 50, or 100 μm in all four corners (symmetric) or in only the two downstream corners (asymmetric). Parallel studies were performed using fluid simulation software to compute the velocity fields to identify if the highest velocity region correlates to the p inch-off location from experimental observation. Initial simulation results suggest that the geometry has a role in determining the pinch off location and therefore the formation of the droplet. Careful control of droplet diameter allows one to deliver a known amount of reagent in a specified volume to an area of interest