Influence of microfluidic geometry on micro-droplet formation

Microfluidic technologies open the door to a plethora 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 microdroplets. Microfluidic devices are built using standard soft lithography techniques (Whitesides and coworkers, Electrophoresis, 2000). 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 flow patterns which affect the genesis of the drop itself. The purpose of this work was to study micro-droplet flows in six slightly varying device geometries to better understand the effect of flow patterns on the droplet formation process. The micro-channels in each device are 100 um wide and 100 um deep. The rounding of the corners of the cross-junction was 0, 50, or 100 um in all four corners (symmetric) or in only the two downstream corners (asymmetric). By characterizing how small changes in geometry influence droplet formation you gain insight into how droplet size and volume may change as certain dimensions are altered either by design manipulation or fabrication error