Contribution to the study of the formation mechanism of mesoporous SBA-15 and SBA-16 type silica particles in aqueous acid solutions

Abstract

Dynamic light scattering (DLS) was used to follow the evolution of the micelles of two triblock copolymer surfactants, Pluronic F127 and Pluronic P123, in diluted aqueous reaction mixtures during the formation of respectively SBA-16 and SBA-15 type mesoporous silica particles at different temperatures, acid and salt concentrations. The silica source (tetraethoxysilane TEOS) is adsorbed by the micelles and undergoes hydrolysis. The resulting siliceous species coat the hydrophilic corona of the micelles, transforming those into composite colloids. The shape of the colloids formed from Pluronic F127 remains spherical but their size increases, whereas the spherical shape of the colloids with Pluronic P123 evolutes into an elongated shape. The decrease of the repulsion energy of these composite colloids allows their aggregation into “liquid particles” (spheres or polyhedra), as observed by optical microscopy. The “liquid particles”, which can be re-dissolved in the case of the SBA-16 precursor by decreasing the temperature, transform into the final solid mesoporous silica particles by siloxane bonds formation within the coalesced silica walls.