Control of Pore Sizes in Mesoporous Silica Templated by Liquid Crystals in Block Copolymer−Cosurfactant−Water Systems

Abstract

Colloidal silica has been polymerized in the aqueous domain of lyotropic liquid crystal phases in ternary surfactant (Pluronic F127 or P123)−cosurfactant (butanol, pentanol, or hexanol)−water systems to create optically transparent mesostructured surfactant−cosurfactant−silica monoliths. The use of ternary systems enriches phase diagrams of aqueous surfactant systems, which in turn introduces more flexibility and diversity into the designed synthesis of mesoporous materials. Lyotropic surfactant liquid crystal phases are preserved throughout the inorganic polymerization and gelation processes and directly template the formation of inorganic mesophases. The cosurfactant chain length and the cosurfactant/surfactant mass ratio have been used to control the pore size. The large shrinkage of mesopores during calcination can be reduced with hydrothermal treatment prior to calcination. Highly ordered mesoporous silica samples with identical pore sizes, but very different wall thickness, can be prepared. The removal of surfactants and cosurfactants gives periodic hexagonal mesoporous silica with excellent thermal and hydrothermal stability.