Time-Dependent Nanoemulsion Droplet Size Reduction By Evaporative Ripening

To overcome limitations of flow-induced rupturing and obtain nanodroplet sizes approaching the micellar scale, we make oil-in-water nanoemulsions having a dispersed phase that contains lower- and higher-molecular-weight oils. After nanoemulsion formation by extreme flow-induced droplet rupturing, the nanodroplets become even smaller as molecules of the lower-molecular-weight oil migrate out of the droplets into the aqueous continuous phase and are removed by evaporation while stirring. We control the degree of reduction primarily through the volume fraction of higher-molecular-weight oil originally present in the dispersed phase. We study the droplet size reduction rate using time-dependent dynamic light scattering. This method is useful for making nanodroplets containing extremely viscous high-molecular-weight liquids that would be difficult to emulsify otherwise. Additionally, we recover the evaporated lower-molecular-weight oil by distillation and reuse it in subsequent emulsification, thus demonstrating an environmentally friendly method for mass-producing extremely small nanodroplets.