SYNTHESIS OF NANOPOROUS SILICA WITH NEW PORE MORPHOLOGIES BY TEMPLATING THE ASSEMBLIES OF IONIC BLOCK-COPOLYMERS

Mesoporous silicas with variable pore size and architecture were made by using aqueous solutions of block copolymers with one polyelectrolyt e 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 origina l self-assembly structure. In this paper, three cationic polybutadiene -b-poly(vinylpyridinium) block copolymers as well as an anionic poly(e thylethylene)-b-polystyrenesulfonate block are utilized as structure-d irecting media. Depending on the relative block lengths and the salt c ontent in the reaction mixture, different aggregation structures are o btained, leading to well-defined spherical pores in the size range bet ween 10 nm < xi < 50 nm or more complex architectures, such as ''rattl es'', the casts of multilamellar vesicles. It is proposed that it is p ossible to use this precise silica casting procedure in order to depic t 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 sys tems.