Preparation, physico-chemical characterization and transport properties of block copolymer-templated silica coatings

Highly selective silica membranes with controlled porosity can be obtained by employing organic/inorganic mixed micellar solutions based on the use of commercial templates. Among others, amphiphilic block copolymers are very attractive materials as structure directing agents [1]: 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 template blocks, and on solution parameters. Silica porous films described in this contribution were 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 both pore sizes and alignment in the final material, many different variables were changed: e.g. block copolymer chain length, block copolymer/TEOS ratio, hydrophilic/hydrophobic solvent ratio and use of additives (i.e. polystyrene homopolymer). Moreover, by changing the block copolymer/TEOS ratio, it was possible to obtain reverse micellization and formation of silica nanoparticles. By spin-coating deposition of such nanoparticles onto a macroporous inorganic substrate (followed by calcination) [2] an organized porous layer was obtained, thus generating a depth filter system whose porosity is due to inter-particle voids. Transport measurements involving these porous functionalized devices were realized and promizing results were obtained for applications in the field of microfluidics for separation, detection and dosing of chemicals. [1] R. Nisticò, D. Scalarone. G. Magnacca, Microporous and Mesoporous Materials 190 (2014) 208-214. [2] R.G. Juez, V. Boffa, D.H.A. Blank, J.E. ten Elshof, Journal of Membrane Science 323 (2008) 347-351.