Janus Particles Synthesis by Emulsion Interfacial Polymerization: Polystyrene as Seed or Beyond?

New strategies for synthesis of Janus particles are of essential importance in the advancement of material science and technology. However, it remains a great challenge to synthesize uniform Janus particles with controllable topological and chemical anisotropy. To overcome this challenge, we have recently developed a general emulsion interfacial polymerization approach. This approach can be applicable to a wide variety of vinyl monomers, including positively charged, neutrally charged, and negatively charged monomers. Different from the traditional seed swelling emulsion polymerization that usually involved using cross-linked polystyrene (PS) particles as seeds to produce Janus particles, we preloaded non-cross-linked PS particles in the emulsion system to construct an interfacial polymerization system. However, the role of these non-cross-linked PS particles in the emulsion interfacial polymerization is unclear. In this work, we revealed the role of non-cross-linked PS particles preloaded in emulsion interfacial polymerization for fabricating uniform Janus particles with controllable topology. We found that the introduction of non-cross-linked PS particles could significantly control the topology and uniformity of Janus particles. Theoretical simulation results by dissipative particle dynamics simulation coupled with stochastic reaction model revealed that the polymer chains of PS inside oil droplets play a decisive role in the topographic control of Janus particles. These hydrophobic PS chains could slow down the polymerization inside oil droplets due to shielding effect of the PS chains to the newly formed poly(styrene divinylbenzene) (PSDVB) nucleus. Meanwhile, we demonstrated that the diverse topology features of Janus particles could be tuned by regulating the concentration of PS polymer and monomers. These results may help us to comprehensively understand the mechanism of emulsion interfacial polymerization methodology and design new functional particle materials.