Tuning Composition of Multicomponent Surface Nanodroplets in a Continuous Flow-In System

Droplets are excellent platforms for compartmentalization of many processes such as chemical reactions, liquid–liquid extraction, and biological or chemical analyses. Accurately controlling and optimizing the composition of these droplets is of high importance to maximize their functionality. In this work, the formation of multicomponent droplets with controllable composition by employing a continuous flow-in setup is demonstrated. Multiple streams of different oil solutions are introduced and mixed in a passive flow mixer and the outcoming mixture is subsequently fed into a flow chamber to form surface nanodroplets by solvent exchange. This method is time-effective, enabling programmable continuous processes for droplet formation and surface cleaning. The surface nanodroplets are formed within 2.5 min in one cycle, and the droplet formation is reliable with similar size distribution over multiple cycles. The composition of the resulting surface nanodroplet can be tuned at will simply by controlling the flow rate ratios of each stream of the oil solution. Using fluorescence imaging, it is shown that the composition of the binary surface nanodroplets agrees well with theoretical values predicted using the phase diagram.