Hybrid Emulsion-Dispersion (HED) Polymerization Enables One-Pot Synthesis of Functional Janus Nanoparticles

Janus nanoparticles possess anisotropic architectures that enable strong interfacial interactions and enhanced functionality, yet their synthesis often depends on multistep seeded or templated routes. Here we report hybrid emulsion-dispersion (HED) polymerization, a one-pot strategy that introduces a fundamentally different route to Janus morphology by inducing symmetry breaking via polymerization-induced phase separation in a single reactor. This process directly yields polymeric Janus nanoparticles without seed preparation, sequential monomer addition, or post-modification. Kinetic studies and a morphology map reveal that symmetry breaking is established within the first minutes of polymerization, while the final morphology is governed by the balance between solubility, interfacial energy, and kinetic arrest. This strategy produces sub-200 nm Janus nanoparticles with tunable morphologies and compositions. As a proof of concept, we synthesize N-halamine-functional Janus nanoparticles via HED and demonstrate their effectiveness in coatings. The particles preferentially enrich at coating interfaces and enable efficient, rechargeable antibacterial activity.