A green and scalable route to water-in-water emulsion stabilizers using photoenzymatic polymerization-induced self-assembly

Water-in-water (w/w) emulsions are biphasic all-aqueous systems with promising applications in bioreactors and drug delivery. However, their stabilization is challenging due to an extremely low interfacial tension. We report a green and scalable strategy based on photoenzymatic reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion copolymerization to prepare well-defined diblock copolymer nanoparticles and demonstrate their efficacy as stabilizers for w/w emulsions. Using poly(N,N-dimethylacrylamide) as a macromolecular chain transfer agent, we synthesized a series of spherical nanoparticles with controlled molecular weights and tunable diameters via statistical copolymerization of diacetone acrylamide with N,N-dimethylacrylamide. These sterically-stabilized nanoparticles effectively stabilize w/w emulsions composed of immiscible aqueous solutions of poly(ethylene glycol) and dextran. Notably, nanoparticles of intermediate diameter (Dh = 199 nm) conferred extraordinary stability, maintaining emulsion stability for more than 50 h. This study establishes an environmentally benign and scalable approach to prepare tailorable nanoparticles for biocompatible w/w emulsions, which offer potential biomedical applications.