Hollow silica and silica-polymer spheres with diameters between 720 and 1000 nanometers were fabricated by consecutively assembling silica nanoparticles and polymer onto colloids and subsequently removing the templated colloid either by calcination or decomposition upon exposure to solvents. Scanning and transmission electron microscopy images demonstrate that the wall thickness of the hollow spheres can be readily controlled by varying the number of nanoparticle-polymer deposition cycles, and the size and shape are determined by the morphology of the templating colloid. The hollow spheres produced are envisioned to have applications in areas ranging from medicine to pharmaceutics to materials science.
Caruso et al. (1998) studied this question.