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. Particular insight is provided regarding the importance of tuning the ionic species present at the NP/IL interface; In this work we compare the effect of Li+, Na+ or Rb+ ions. The nature of these species has here a clear influence on the short-range spatial organization of the ions at the interface and thus on the colloidal stability of the dispersions, governing both the NP/NP and NP/IL interactions, which are here both evaluated. The overall NP/NP interaction is either attractive or repulsive. It is characterized by determining, thanks to the SAS techniques, the second virial coefficient A2, which is found independent of temperature. The NP/IL interaction is featured by the dynamical effective charge ξoeff of the NPs and by their entropy of transfer SˆNP (or equivalently their heat of transport QˆNP) 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.