Characterization of micro-droplet formation: experiment and simulation

Microfluidic technologies are an innovative application for biological and chemical systems. The Microfluidic environment is ideal because of its controlled physics for reproducible laminar flow. 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). Microdroplets allow an accurate and consistent amount of reagent for certain applications. There are slight differences produced in the geometries in tolerances and non-uniformity during fabrication steps. This work studies the formation of microdroplets using six geometries to understand flow patterns on the formation of mono-disperse droplets. The rounding of the corners of the cross-junction was 0, 50, or 100 microns 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 pinch-off location from experimental observation. Initial simulation results suggest that the geometry has a role in determining the pinch off location and therefore influences the formation of the droplet. Initial simulations suggest that the pinch-off point correlates with the cross-junction’s downstream rounding rather than the incoming flow rates. Experimental data however indicates there are differences in the pinch off location at different flow rates. Statistical analysis of the droplet formation diameter and the pinch-off location were conducted to test if the are significant differences in experimental results for varying flow conditions. The cross-junction’s upstream rounding is found to influence the droplet diameter. Careful control of the droplet diameter allows delivery of a known amount of reagent in a specified volume to an area of interest