(634g) Nanofiltration Membranes From Oriented Mesoporous Silica Thin Films

Metal oxide membranes synthesized by sol gel templating have the potential to be versatile platforms for separations on the basis of the ability to control the pore size by templating, the range of available approaches to functionalize the pores, and the stability of the membranes in the presence of different chemical and biological environments.  Mesoporous thin film silica templating typically leads to parallel pore alignment with respect to the surface, and therefore inaccessible pores in the potential membrane structure.  Recent advances in thin film synthesis provide for perpendicular pore alignment using chemically neutral surfaces.  In this work, orthogonal thin film silica membranes are synthesized on alumina supports using block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as the template.   The orthogonal pore structure, which is achieved by sandwiching the membranes between two chemically neutral surfaces, is consistent with X-ray diffraction results and pore accessibility is demonstrated by solvent flux through the membrane. For the first time, the ability of these thin silica films to separate solutes by size exclusion is demonstrated.   A protein, bovine serum albumin (BSA), is used as a model system to demonstrate that these films provide an adequate separation by preventing diffusion through the membrane. 5 (6)-Carboxyfluorescein and FITC-tagged dextrans of differing sizes are used to determine the permeability of the membrane as well as the approximate radius of the pores. The FITC-tagged dextrans of varying sizes are used again to show that size cut off occurs around a molecular weight of 40,000 Daltons. These membranes show much promise for applications in catalysis, bio-sensing, and affinity separations.