Continuous Production of Water‐Soluble Nanocrystals through Anti‐Solvent Precipitation in a Fluidic Device

Abstract This paper describes a simple and robust method for the continuous production of water‐soluble nanocrystals using anti‐solvent precipitation under diffusion control in a fluidic device. We use sodium chloride (NaCl) as an example to demonstrate the concept. In a typical process, aqueous NaCl and ethanol (the anti‐solvent) serve as the focused and focusing phases, respectively, for the generation of a coaxial‐flow system. Upon contact with each other, the rapid diffusion between water and ethanol leads to the formation of NaCl nanocrystals at the interface while a gradient in NaCl concentration is created along the flow direction. The nucleation and growth of NaCl nanocrystals can be readily tuned by varying the hydrodynamic parameters such as the ratio between the flow rates of the two phases and the total volumetric rate. By optimizing these parameters, we are able to produce NaCl nanocubes and nanospheres as small as 20 nm and 6 nm, respectively, while attaining a narrow distribution in size. We have also successfully generated KCl nanocrystals with similar controls, demonstrating the generality of this method for the production of water‐soluble nanocrystals.