Tuning the Solid/Liquid Interface in Ionic Colloidal Dispersions: Influence on their Structure and Thermodiffusive Properties

We focus here on the relationship between the physicochemical properties of electrostatically stabilized colloidal dispersions and the nanoparticles/solvent interface. Dispersions of maghemite (γ-Fe2O3) in polar solvents, here water and dimethyl sulfoxide (DMSO), are prepared with a new process that enables tuning easily this interface. Departing from the point of zero charge (PZC), the nanoparticles (NPs) are charged in a controlled way by adding acid or base. This pathway enables control of the surface state of the nanoparticles, i.e., the NP’s charge and the nature of the counterions, as well as the amount of free electrolyte in the dispersion. Stable dispersions are obtained because of electrostatic repulsion, in water and in DMSO, with electrolyte concentrations up to 20–40 mM. Small angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques are here applied to concentrated dispersions in order to understand the nanostructure and quantify the interparticle interactions. Specific ioni...