Optical properties of ordered macroporous materials made by colloidal assembly

Periodic macroporous silicon dioxide and titanium dioxide were made using monodisperse polystyrene as templates and ultrafine metal oxide particles as the surrounding high dielectric material. The process involves slowly drying a monodisperse polystyrene dispersion with a colloidal dispersion of the desired oxide. As the mixture is drying, the polystyrene spheres organize themselves in an ordered lattice and the oxide particles pack into the voids between the spheres. Subsequent removal of the polystyrene by heat treatment leads to an ordered macroporous material with the oxide particles forming the walls of the pores. Optically, these materials exhibit a strong iridescence in reflected light. Optical reflectivity measurements were made to prove the existence of band gaps in the material.