Anomalous Locomotion and Precise Self-positioning of Nanoparticles on Faceted Liquid Emulsion Droplets

Decorating emulsion droplets by particles stabilizes foodstuff and pharmaceuticals. Interfacial particles also influence aerosol formation, thus impacting atmospheric CO₂ exchange. While particles at disordered droplet interfaces were extensively investigated, those at the ubiquitous ordered interfaces have never been studied.

We study the dynamics of tracer colloidal particles, incorporated into a curved 2nm-thick crystal, forming at T=T_s≈26 ^oC at the interface of liquid oil-in-water emulsion droplets. We demonstrate the particles to be spontaneously dragged to particular surface locations. We identify these particle "attractors" with topological defects within the crystalline structure. At T=T_d < T_s, the droplets undergo an unprecedented sphere-to-icosahedron shape transformation, with their bulk remaining liquid. At the transformation temperature, the attractors self-position onto the vertices of the icosahedra and fix there the positions of the surface-adsorbed particles. At an even lower temperature, the particles are spontaneously expelled from the droplets. These phenomena allow functional liquid “atoms” to be designed, with their “valency” fixed by precise temperature-tuned positioning, and type, of the interfacial ligands, enabling self-assembly into supra-“atomic” nano-structures. Our observations also impact upon the understanding of protein positioning on cell membranes, controlling essential biological functions.