Structural properties of silica gels prepared with additions of surfactants

Abstract

The micelle structure of ionic and nonionic surfactants has allowed the employing of such substances as templates for preparation of silica-based mesoporous materials, with interesting structural properties. The structuring of the micelles can form ordered templates for precipitation or phase separation, or yet gelification during hydrolyze and condensation reactions of silicon alkoxides, yielding structures of great scientific and technological interest in several areas of the knowing, such as catalyze, separation, adsorption, enzyme immobilization, controlled drug driven and delivery, and in the nanotechnology, working as adequate matrices for nanoparticle preparation of advanced materials. Among the nonionic surfactants we found the tri-block poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic P123) copolymer, which has been employed extensively in the preparation of a series of ordered mesoporous silica. Sodium Dodecyl Sulfate (SDS) is a very popular surfactant, although there are only a few references reporting its employing as templates for obtaining mesoporous silica. In this work, we study the structural properties of silica prepared from TEOS hydrolysis with additions of surfactants, namely the nonionic P123 and the ionic SDS surfactants. The concentration of the surfactants should be varied within the ranges in which precipitation of silica should occur and in which the phase separation should pass by processes of a gel formation. The structural characteristics are studied through measures of density, thermal analysis (DTA, TG, DSC), nitrogen adsorption isotherms, DSC thermoporometria, small-angle X-ray scattering (SAXS), and mercury porosimetry. (AU)