Ion specific tuning of nanoparticle dispersion in an ionic liquid: A structural, thermoelectric and thermo-diffusive investigation

Dispersions of charged maghemite nanoparticles (NPs) in EAN (ethylammonium nitrate) a reference Ionic Liquid (IL), are here studied using a number of static and dynamical experimental techniques; Small Angle Scattering (SAS) of X-rays and of Neutrons, Dynamical Light Scattering and Forced Rayleigh Scattering. A particular insight is given to the importance of tuning the ionic species present at the interface NP /IL; In this work we compare the effect of Na+, Rb+ or Li+ ions. The nature of these species have here an influence on the short-range spatial organization of the ions at the interface and thus on the colloidal stability of the dispersions. They govern both the NP/NP and the NP/IL interaction, which are here both characterized. The short-range global NP/NP interaction is either attractive or repulsive. It is characterized by the determination of the second virial coefficient A2 thanks to the SAS techniques and which is found independent of temperature. The NP/IL interaction is characterized by the dynamical effective charge ξoeff of the NPs and by their entropy of transfer SˆNP determined here thanks to thermoelectric and thermodiffusive measurements. For repulsive systems, a temperature dependence through an activated process is obtained for these two latter quantities.