Dispersions of magnetic nanoparticles in the mixture ethyleneglycol-choline chloride: The role of solvent association

The mixture of choline chloride and ethyleneglycol ((1:3) on the molar scale) is first characterized using density, viscosimetry and refractive index measurements, in the temperature range 20-45°C, with controlled amounts of water. Thermodynamic parameters such as the activation entropy, enthalpy and Gibbs energy for the viscous flow are deduced from the data and show that the solvent is highly structured. A protocol to disperse in this solvent 10 nm maghemite nanoparticles previously synthesized in water is described. The good quality of the dispersion is assessed by visual observations, optical microscopy, small angle X-ray scattering (SAXS), magnetization measurements, viscosimetry, and light scattering. The results lead to the description of a local viscosity around the particles, lower than the macroscopic one, that could be the result of the solvent segregation with ethyleneglycol being mostly present in the close vicinity of the particles.