Generation of sub-micron-sized droplets, by continuous extensional flow

A method is devised to generate sub-micron-sized droplets without surfactants by using a continuous extensional flow. By using the extensional flow judiciously the physical limits on the viscosity ratio of the dispersed and dispersing media could be overcome. The strain hardening behavior of the Boger fluid under the extensional flow gave a synergic effect to generate the smaller droplets. It was shown that the drop size could be decreased to a sub-micron scale and the droplet size distribution was much narrower compared to the case of the conventional shear (stirring) method. This method is also applicable when the two phases are compatible.