Synthesis of Nanoporous Silica with New Pore Morphologies by Templating the Assemblies of Ionic Block Copolymers

Abstract

Mesoporous silicas with variable pore size and architecture were made by using aqueous solutions of block copolymers with one polyelectrolyte block as templates in a sol-gel process. Pore size and connectivity follow the structure of the block copolymer micelles or mesophases, i.e., the resulting silica gel network is a precise copy of the original self-assembly structure. In this paper, three cationic polybutadiene- b -poly(vinylpyridinium) block copolymers as well as an anionic poly(ethylethylene)- b -polystyrenesulfonate block are utilized as structure-directing media. Depending on the relative block lengths and the salt content in the reaction mixture, different aggregation structures are obtained, leading to well-defined spherical pores in the size range between 10 nm < ξ < 50 nm or more complex architectures, such as “rattles”, the casts of multilamellar vesicles. It is proposed that it is possible to use this precise silica casting procedure in order to depict and characterize unknown aggregation structures of block copolymers. Therefore silica casting appears to be a considerable alternative to the more tedious freeze-fracture preparations of similar colloidal systems.