Design of Ion-Containing Polymer-Grafted Nanoparticles for Conductive Membranes

While sulfonated polymers are commonly used in membranes for fuel cells and water filtration applications, challenges of controlling ionic aggregation and understanding morphology effects on conductivity and transport still remain. In this work, we investigate the aggregation of copolymer-grafted nanoparticles that are designed to form conductive structures with low sulfonation amounts of chains. We demonstrate that long grafts of polystyrene chains with sulfonated end groups form side-by-side aggregated strings and retain their structures in ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide [HMIM][TFSI]. Transmission electron tomography results revealed that these aggregates are monolayers of particles at low sulfonations and planar-like networks at 3 mol % sulfonation in the ionic liquid. Organization of magnetic nanoparticles with the polymer grafting approach is shown, for the first time, to enhance conductivity upon incorporation of an ionic liquid.