The presently disclosed subject matter provides methods for continuously generating uniform polyelectrolyte complex (PEC) nanoparticles comprising: flowing a first stream comprising one or more water-soluble polycationic polymers at a first variable flow rate into a confined chamber； flowing a second stream comprising one or more water-soluble polyanionic polymers at a second variable flow rate into the confined chamber； and impinging the first stream and the second stream in the confined chamber until the Reynolds number is from about 1,000 to about 20,000, thereby causing the one or more water-soluble polycationic polymers and the one or more water-soluble polyanionic polymers to undergo a polyelectrolyte complexation process that continuously generates PEC nanoparticles. Compositions produced from the presently disclosed methods and a device for producing the compositions are also disclosed.
