From Responsive Interfaces to Honeycomb Membranes by Controlled Radical Polymerisation

Abstract: In this study, surface modification of both organic and inorganic substrates (in terms of cellulose and silica nanoparticles, respectively) has been explored using surface-initiated atom transfer radical polymerisation (ATRP).The desire to modify bio-based materials to fit into new application areas and the need for bio-based materials with improved material properties is steadily increasing due to environmental concern.Superhydrophobic and self-cleaning cellulose surfaces were fabricated by combining ATRP with post-functionalisation. Glycidyl methacrylate was grafted from filter paper, and the epoxide groups were used as reactive handles to create a branched “graft-on-graft” architecture. Post-functionalisation of this architecture with perfluorinated chains or alkyl chains resulted in the formation of superhydrophobic surfaces.Grafting of N-isopropylacrylamide (NIPAAm) from filter paper yielded cellulose surfaces capable of switching the wettability, from hydrophilic to hydrophobic, in response to changes in temperature. The wettability of cellulose surfaces grafted with poly(4-vinylpyridine) (P4VP) could be adjusted from hydrophilic to hydrophobic by changing pH. Furthermore, cellulose surfaces responding to changes in both pH and temperature were obtained via grafting of block copolymers of PNIPAAm and P4VP.The use of inorganic nano-particles in composites has attracted considerable academic and industrial interest due to their excellent mechanical and thermal properties. Styrene was grafted from the surface of silica nanoparticles using ATRP. The resulting organic-inorganic hybrid materials did not aggregate to the same extent as the un-modified silica particles.The polystyrene-modified silica particles were used for the fabrication of honeycomb membranes. It was evident that the pore sizes and the number of porous layers could be tuned by varying the conditions used for film casting. To broaden the range of polymers available for film casting into honeycomb membranes, a block copolymer of polystyrene and poly(methyl methacrylate) was grafted from silica nanoparticles. Polymer-blends of polystyrene-modified particles and poly(9,9´-dihexylfluorene) (PDHF) were also used as an alternative to incorporate functionality into honeycomb membranes.