Colloidal photonic crystals obtained by the Langmuir–Blodgett technique

Monodispersed silica spheres with diameters of 220–1100 nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic medium in the presence of water and ammonia. By grafting vinyl or amine groups on silica surfaces using the coupling agents allyltrimethoxysilane and aminopropyltriethoxysilane, respectively, amphiphilic silica spheres were obtained and could be organized to form a stable Langmuir film at the air–water interface. The control led transfer of this monolayer of particles onto a solid substrate gave us the ability to build three-dimensional regular crystals with well-defined thickness and organization. These colloidal crystals diffract light in the UV, visible and the near-infrared (NIR) spectral regions, depending on the size of the silica spheres and according to the Bragg’s law.