Synthesis of mesoporous silica films by block copolymers micellization

Highly selective silica membranes with controlled porosity can be obtained by employing organic/inorganic mixed micellar solutions based on the use of commercial templates. Amphiphilic block copolymers are very attractive materials as structure directing agents. When mixed with organic solvents selective for one of the blocks, they can self-assemble into micelles with the insoluble blocks constituting the micellar core. The morphology and size of self-assembled micelles depend on the size (length) and nature (polarity) of the templates blocks, and on solution parameters. Silica porous films described in this contribution are obtained by sol-gel reaction of tetraethyl orthosilicate (TEOS) using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) copolymers as templates. In order to modulate pore sizes and alignment in the final material, many different variables are changed: e.g., block copolymer chain length, block copolymer/TEOS ratio, solvents, hydrophilic/hydrophobic solvent ratio and use of additives (i.e. polystyrene homopolymer). To obtain an oxidic mesoporous membrane, the block copolymer/TEOS micellar solution is deposited on inorganic supports via spin-coating. The spin coating conditions used ensure fast evaporation of solvents, freezing in the solid state the micelles shape present in solution. Block copolymer micelles are finally removed by thermal degradation in air, leaving an amorphous porous material which can be applied in the field of microfluidics for separation, detection and dosing of molecules, ions, charged nanoparticles or biomolecules.