Reversible Formation of Nanoporous Colloidal Membranes Via Self-Assembly

We prepared nanoporous membranes using self-assembly of silica colloidal spheres surface-modified with acrylate polymer brushes carrying acidic (sulfonic) or basic (quaternized amines) groups. The membranes were prepared by mixing the polymer-modified silica spheres of the opposite charge followed by their vertical or horizontal deposition from suspension and air-drying. The mechanical stability of the resulting membranes is due to non-covalent acid-base interactions between the polymer brushes, while the porosity results from the presence of the hard colloidal nanoparticles. The membrane nanopore size can be controlled in the 5-50 nm range by varying the silica sphere size and the length of the polymer brushes.

The membranes are lightweight, durable and stable in a variety of organic solvents, where they have been used for model separations. The membranes can be easily disassembled by changing the solvent to water, which disrupts the acid-base interactions and leads to re-dispersion of the polymer-modified silica spheres comprising the membranes. The membranes can be reassembled again by deposition from the suspension. Hydrophobic side chains can be introduced into the polymer brushes to tune the assembly of the membranes in various solvents.