Formation of dispersions using ‘‘flow focusing’’ in microchannels
The paper discusses a way to produce dispersed liquid droplets in a continuous liquid phase utilizing a flow-focusing geometry. Monodisperse emulsions are produced over a range of flow rates and found to be approximately the size of the orifice. Biodisperse and polydisperse droplet distributions are generated at higher outer flow rates and lower inner to outer flow rate ratios. They also found that the smallest droplets produced can be much smaller than the orifice radius.
Soft matter example
The use of Span 80 surfactant (Sorbitan monooleate) in the outer (oil) phase helps stabilize the droplets and thus making it harder for the droplets to coalesce.
In small channels such as the one used in the experiment, wetting properties of the fluids used and the channel materials become important. These properties determine how the fluids behave (ie. squeezing or dripping at a certain flow rate).