The separation of microsized oil droplets from water is strongly required by the environmental protection and petroleum industry. However, the separation of microsized oil droplets from water is often ignored. Herein, magnetic Janus particles are reported with a convex hydrophilic surface/concave oleophilic surface by emulsion interfacial polymerization and selective surface assembly, realizing the rapid and efficient separation of microscaled tiny oil droplets from water. These magnetic Janus particles exhibit significant abilities to separate microscaled oil droplets from water, which usually occurs within 120 s with a separation efficiency >99%. Theoretical and experimental results demonstrate that these magnetic Janus particles can capture tiny oil droplets to make them coalesce into larger ones during the process of separation. Further studies reveal that these Janus particles can self-assemble and closely pack onto the interface of larger oil droplets, acting as surfactants to stabilize them. Moreover, the shape effect of the Janus particle is demonstrated on the coalescence of the oil droplets.particles are fabricated by emulsion interfacial polymerization between hydrophilic acrylic acid (AA) and oleophilic styrene/ divinyl benzene (St/DVB) followed by selective electrostatic assembly of Fe 3 O 4 nanoparticles on the convex surface of the resulting Janus particles. These magnetic Janus particles exhibit a remarkable ability to rapidly separate tiny oil droplets from water with a high separation efficiency (>99%). The influence of the interfacial activity of Janus particles with different shapes on the oil-water separation is comprehensively investigated. Results and DiscussionMagnetic Janus particles were fabricated by emulsion interfacial polymerization and interfacial assembly (Figure 1a). The

Precise synthesis of polymer particles with topology and surface chemistry spanning from isotropy to anisotropy is critically needed for the fundamental research and industrial production. Herein, we report a seed wettability-manipulated emulsion interfacial polymerization to precisely synthesize polymer particles spanning from anisotropic Janus particles to spherical heterogeneous nanoporous particles. The variation of seed wettability from hydrophobicity to hydrophilicity allows a topological transition of obtained polymer particles from anisotropic Janus particles to spherical heterogeneous nanoporous particles, along with the distribution of surface chemistry. This large-span evolution of topology and surface chemistry of obtained particles is due to the shifting of the initially polymerizable emulsion interface from oil-in-water (O/W) to water-in-oil-in-water (W/O/W) driven by osmotic pressure. This seed wettability-manipulated emulsion interfacial polymerization is applicable to a variety of hydrophobic/hydrophilic monomer pairs, allowing flexible fabrication of diverse Janus particles and heterogeneous nanoporous particles.