Janus Colloids via Electroless Deposition of Metal on Interfacially Confined Particles

Janus particles provide a powerful platform for studying asymmetric surface functionality and active colloidal matter, yet their broader utilization is hindered by the lack of fabrication strategies that offer quantitative and independent control over patch geometry. Here, we report an interfacial confinement-assisted electroless deposition process that exploits irreversible particle adsorption at the liquid-liquid interface for directed metal deposition. This process enables systematic control over metal patch thickness (5-50 nm) and surface coverage while remaining robust to the deposition of various metals (Au, Ag, Pt, Ni, Cu) and scalable across centimeter-scale interfacial areas (≈ 16 cm2). The generality of the approach is demonstrated by the synthesis of Janus particles with varied shapes (sphere, ellipsoid, peanut, sphero-cylinder, cube) and surface chemistries (hematite, silica, polystyrene, p-NIPAM) at liquid-liquid interfaces formed with different oils. To characterize the activity of particles, we perform experiments in hydrogen peroxide solutions of varying concentrations and demonstrate the influence of the catalytic patch thickness on the self-propulsion of Janus particles. Because the proposed process relies on general principles of colloids and interfacial chemistry, it is readily extendable to diverse systems and provides a versatile chemical route to architected Janus colloids.