Engineering of silica monoliths and the effect of clay doping on their properties

Abstract

Covalent cross-linking of colloidal silica particles under controlled conditions by the α,ω-bridging organosiloxane (CH₃O)₃Si(CH₂)₂Si(OCH₃)₃ leads to highly transparent silica monoliths. Addition of a small amount of clay nanoparticles to the sol enables fine-tuning of the optical properties of the monoliths based on the size of the clay particles. In a second approach, use of electrostatic assembly between negatively charged colloidal silica particles and a positively charged silicone surfactant, leads to silicone coated/linked silica particles in which the inorganic building units can be assembled into shaped porous networks, thus affording lightweight silica monoliths after calcination. Addition of a small amount of clay nanoparticles to the silica produces lightweight clay–ceramic composites with improved mechanical properties without any appreciable changes in density.