Formation of dispersions using ‘‘flow focusing’’ in microchannels

A flow-focusing geometry is integrated into a microfluidic device and used to study drop formation in liquid–liquid systems. A phase diagram illustrating the drop size as a function of flow rates and flow rate ratios of the two liquids includes one regime where drop size is comparable to orifice width and a second regime where drop size is dictated by the diameter of a thin ‘‘focused’’ thread, so drops much smaller than the orifice are formed. Both monodisperse and polydisperse emulsions can be produced.