Fabrication of Janus Supraparticles by Induced Phase Separation by Gravity

Janus supraparticles, which are anisotropic colloidal assemblies with phase-separated domains, have attracted significant interest for their structural and functional versatility. However, fabricating Janus supraparticles is challenging because it requires precise control over the spatial arrangement of different micro- or nanoparticles within a single assembly. While phase separation of a nanoparticle mixture with an external gradient field is studied with magnetic particles, gravity is unexplored as a potential external field. In this work, we demonstrate the synthesis of Janus supraparticles by evaporation of binary suspensions on a superamphiphobic substrate. We find that combining particles of similar size but different densities, as well as those of the same material with varying sizes, leads to an effective internal phase separation. These results highlight the potential of leveraging sedimentation as a particularly simple yet robust strategy to induce spatial heterogeneity during supraparticle formation.