Synthesis and physico-chemical characterization of porous silica membranes obtained by using PS-b-PEO block copolymers as soft templating agents

Highly selective membranes with controlled porosity can be obtained by growing thin films of mesoporous oxides on an appropriate support. This can be achieved employing organic/inorganic mixed micellar solutions based on the use of commercial or ad hoc designed templates. Amphiphilic block copolymers are very attractive materials as soft-templating 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 and the soluble ones the corona. The morphology and size of self-assembled micelles depend on the size (length) and nature (polarity) of the blocks, and on solution parameters. Silica porous membranes described in this contribution were obtained by sol-gel reaction of a silicon oxide precursor (TEOS) and using polystyrene-block-poly(ethylene-oxide) (PS-b-PEO) block copolymers as templates. In order to modulate pore sizes and alignment of the final material, many different variables were changed: e.g. block copolymer chain length, block copolymer/TEOS ratio, type of solvents, solvent ratio and use of additives (i.e. polystyrene homopolymer). Aim of the present work is the preparation of silica membranes with narrow pore size distribution and high porosity to be applied in the field of microfluidic analyses and as selective gates in microchip-based technologies for separation, detection and dosing of molecular or ionic species, charged nanoparticles or biomolecules.