Disordered structures with short-range correlation exhibit unique photonic or thermal properties, often arising from the self-assembly of monodisperse microspheres. Colloidal clusters, aggregates of a defined number of microspheres, have anisotropic shapes and offer a unique approach to tailor the short-range correlation compared to traditional isotropic microspheres. However, this potential remains largely unexplored. To this end, we have prepared triangular and tetrahedral colloidal clusters and coassemble them with polystyrene microspheres into both monolayers and thick films (∼10 μm) over 5 mm × 5 mm areas. Through combining scanning electron microscopy images and laser scattering measurements, we show that increasing cluster concentration from 0% to 40% increases disorder in both thin and thick films. Beyond 40%, the short-range order in thin films plateaus, while it increases with triangular clusters but decreases with tetrahedral clusters in thick films. The distinct roles of triangular and tetrahedral clusters offer new insights into design of correlated disordered materials for novel applications.
Synthetically colloidal clusters with new functions and well-controlled size distribution can in principle be constructed using colloidal particles. The building units could be integrated into dense-packed and desired structured with novel functions by means of an efficient strategy or binding patterns. Here we synthesized colloidal clusters of icosahedrons and long-range ordered face-centered cubes (FCCs) via emulsion self-assembly using fluorescence upconversion nanoparticles NaGdF 4 : Yb 3+ , Er 3+ as building blocks. The icosahedrons and FCCs structure may generate spontaneously due to an entropy-driven process. The morphology and structure of colloidal clusters have noticeable transformation from icosahedron-like symmetry to FCC symmetry with the increasing size of clusters. Furthermore, the colloidal clusters could be decorated with cationic polyethyleneimine (PEI) via electrostatic interaction . When copper ions are added, the amino groups of PEI could coordinate with Cu 2+ forming low toxic PEI-Cu 2+ layers, which can further serve as energy receptors to quench upconversion fluorescence with 980 nm laser excitation. Our results reflect that the colloidal clusters not only can serve as a fluorescence platform of detection and analysis but also may represent advancement in the field of colloidal and interface sciences .
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