Encapsulation of Oil Droplets Using Film-Forming Janus Nanoparticles

Polymer Janus nanoparticles with one hard cross-linked polystyrene lobe and one soft film-forming poly(methyl methacrylate-co-butyl acrylate) lobe were synthesized by reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization. The Janus nanoparticles adsorbed to oil/water and air/water interfaces, where the soft lobes coalesced, forming films of thickness between 25 and 250 nm; droplets of silicone oil could be stably encapsulated in polymer in this way. When prepared by mechanical mixing without additives, capsules of diameter 5-500 μm could be prepared, and with additives and application of heat, capsules of diameter around 5 μm were achieved, even with highly viscous silicone oil (20,000 cSt). In a microfluidic device, monodisperse capsules of diameter 180 μm could be formed. The particles were weakly surface-active and spontaneously assembled themselves at air/water interfaces. When added into a paint formula, the oil capsules improved the stain resistance of paint films. Silicone oil leakage from the capsules could be mitigated by incubating the capsules with silica nanoparticles, on which silicone oil reacts, creating grafted layers.