A new technology to form nanoparticles of hydrophobic organic actives at high concentration and yield, and methods to characterize the process are presented. In the Flash Nano Precipitation process, an organic active and an amphiphilic diblock copolymer are dissolved in an organic phase and mixed rapidly with a miscible anti-solvent to trigger precipitation of the active with a narrow particle size distribution and controlled mean particle size (50-500 nm). The enabling components are a novel "analytical" (quantified mixing time) Confined Impinging Jets (CIJ) mixer for millisecond stream homogenization and amphiphilic diblock copolymers, which alter the organic nucleation and growth, provide steric stabilization for the particles, and offer a functional surface for the composite. Methods to quantify fundamental time scales of the process and their relation to component thermodynamics are provided. The technology is useful for applications in enhanced pharmaceutical delivery, dye preparation, and pesticide formulation.