The Formation of Macropores in a Bimodal Silica Synthesized on P123 Block Copolymer as a Template

Abstract

Mechanisms of mesoporous structure formation in materials obtained via the sol–gel synthesis have been rather thoroughly studied in situ by different methods. The study of macropores is commonly carried out after the process is completed. The elucidation of their formation kinetics encounters methodological problems, which remain to be solved. In this work, a simple method has been proposed for studying the formation of macropores in a silica, which is synthesized by using two different precursors on P123 block copolymer as a template via a protocol proposed for SBA-15. In both cases, bimodal materials are obtained, with one of them having the regular mesoporous structure of SBA-15, while the other is amorphous. The method comprises the sampling of the reaction mixture throughout the process, the application of the samples onto the surfaces of glass plates, spin-coating and the removal of solvents and the P123 template by thermal treatment. The analysis of a series of micrographs has shown that, in the silica free of regular mesopores, macropores are formed through phase separation by a binodal mechanism. The features of the macroporous structure formation during the synthesis of SBA-15 have also been discussed. In this case, a rapid phase transition occurs by the spinodal mechanism.