Aggregation of superparamagnetic iron oxide nanoparticles in dilute aqueous dispersions: Effect of coating by double-hydrophilic block polyelectrolyte

Polymer-coated superparamagnetic iron oxide nanoparticles (SPION) in aqueous dispersion were prepared by the coassembly of SPION coated by an oleate bilayer with the double hydrophilic block polyelectrolyte poly[(3,5-bis(trimethylammoniummethy1)-4-hydroxystyrene iodide]-block-poly-(ethylene.oxide) (QNPHOS-PEO) and characterized by TEM and AFM. It was found that the coating by QNPHOS-PEO affects their aggregation into larger structures on the micrometer length scale observed by small-angle light scattering as well as the dynamics of the dispersion observed by dynamic light scattering. Oleate-SPION in aqueous dispersions form compact aggregates with the fractal dimension, D=2.4, and the characteristic size about 2 pm which exhibit internal dynamics manifesting itself by the presence of the relaxation mode with tau similar to q(-3). In the case of QNPHOS-PEO/oleate-SPION dispersions, the polyelectrolyte coating promotes the formation of compact clusters with the size of the order of similar to 10(2) nm. The clusters, weakly interacting by magnetic dipolar interactions, form linear chainlike aggregates with the low fractal dimension, D=1.2. The dynamics of the QNPHOS-PEO/oleate-SPION dispersions observed by DLS is dominated by the diffusion of the clusters. (C) 2015 Elsevier B.V. All rights reserved.