Preparation of free-standing silica 3D colloidal crystal film at water–air interface

A free-standing colloidal crystal film was facilely fabricated at a water–air interface using purified monodispersed SiO2 colloids in a half-close environment. The monodispered silica particles used were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of water and ammonia in ethanol medium. The free-standing film composed of highly ordered three-dimensionally periodic structures exhibited a vivid optical diffraction. The surface tensile force of solution, evaporation, capillary force and the electrostatic interaction of spheres were considered to be the main reason for the self-assembled process of the silica spheres at a water–air interface. The good quality freestanding opal film was anticipated in a diverse field such as photonic crystals and the template of macroporous materials.