Micron-sized spherical aggregates or ‘<i>supraballs</i>’ of hollow silica nanospheres were prepared by emulsion-assisted evaporation-induced self-assembly of polystyrene-silica core-shell nanoparticles and thermal annealing at 600 <sup>o</sup>C for 3 hours. Hollow nanopsheres are smaller than the wavelength of visible light and average interparticle distance between hollow silica is matched with interference resonance condition (d~λ/2) for UV. However, when supraballs are dispersed in solvent of refractive index is matched with silica shell, we found that samples are still white reflecting visible light which may be ascribed to strong multiple scattering from supraballs because effective index of refraction are not matched with solvent. Therefore, we have matched average refractive index of supraballs with that of medium by adjusting mixing ratio in water and ethylene glycol, which showed optically transparent photonic microspheres reflecting UV strongly and selectively.

Visible-transparent and UV-reflective supraballs of hollow silica nanospheres in solution

2019 Fall National Meeting

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