Formation of polyhedral photonic clusters driven by interfacial energy control in confined assembly

The precise fabrication of colloidal clusters with well-defined polyhedral geometries and long-range crystalline order remains a fundamental challenge, constrained by the limited programmability of purely entropy-driven assembly within evaporating droplets. To overcome this limitation, a strategy is introduced in which interfacial energy is manipulated by employing silica nanoparticles (SiO₂) grafted with well-defined polystyrene-block-poly (4-vinylpyridine) (PS-b-P4VP) brushes). This active surface design, coupled with controlled surfactant concentration, allows the manipulate the interfacial free energy of an evaporating emulsion droplet, deliberately steering its deformation from a sphere to a polyhedron. Consequently, polyhedral clusters are successfully fabricated from large nanoparticles (>300 nm). The obtained clusters range from Platonic solids (e.g., tetrahedra, octahedra, and icosahedra) to complex Archimedean and Johnson solids. These structures possess ordered structure consistent with face-centered cubic (FCC) lattice and exhibit vivid structural colors. Furthermore, when integrated with a RuO₂ catalyst, they significantly enhance electrocatalytic oxygen evolution performance. This work establishes interfacial energy as a primary design parameter, moving beyond the entropy-dominated paradigm to enable precise morphology control in confined self-assembly for advanced photonic and catalytic applications.