Effect of Ionic Groups on Polymer-Grafted Magnetic Nanoparticle Assemblies

Conductivity in ionomer melts is governed by the density of conducting ions and ionic aggregation within low dielectric polymers. New material design strategies are needed to direct ion aggregation by utilizing low ion densities that will improve ion conductivity in polymer composite films. Here, we report the dispersion of ionomer-grafted magnetic nanoparticles (NPs) in polymers to explore their potential in energy applications. Iron oxide NPs coated with a uniform silane layer are grafted with polystyrene (PS) chains and are randomly sulfonated to various extents. We examine the interplay between ionic interactions and chain repulsion by varying the ion concentration and length of grafted chains. Transmission electron microscopy and small-angle X-ray scattering results show that ion-containing polymer-grafted NPs form highly ordered chain-like structures below 3 mol % sulfonation in bulk at two particle loadings (5 and 15 wt %). Moreover, increasing grafted chain length leads to long-range spacing correlations between sulfonated strings. This strategy to create discrete and connected highly ordered string nanostructures can be used as a means of controlling the ion aggregation and transport in polymer nanocomposites.