Design of concentrated colloidal dispersions of iron oxide nanoparticles in ionic liquids: Structure and thermal stability from 25 to 200 °C

Hypothesis: Some of the most promising fields of application of ionic liquid-based colloids imply elevated temperatures. Their careful design and analysis is therefore essential. We assume that tuning the structure of the nanoparticle-ionic liquid interface through its composition can ensure colloidal stability for a wide temperature range, from room temperature up to 200 degrees C. Experiments: The system under study consists of iron oxide nanoparticles (NPs) dispersed in ethylmethylimidazolium bistriflimide (EMIM TFSI). The key parameters of the solid-liquid interface, tuned at room temperature, are the surface charge density and the nature of the counterions. The thermal stability of these nanoparticle dispersions is then analysed on the short and long term up to 200 degrees C. A multiscale analysis is performed combining dynamic light scattering (DLS), small angle X-ray/neutron scattering (SAXS/SANS) and thermogravimetric analysis (TGA). Findings: Following the proposed approach with a careful choice of the species at the solid-liquid inter- face, ionic liquid-based colloidal dispersions of iron oxide NPs in EMIM TFSI stable over years at room temperature can be obtained, also stable at least over days up to 200 degrees C and NPs concentrations up to 12 vol% (= 30 wt%) thanks to few near-surface ionic layers. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

By carefully selecting the species at the solid-liquid interface, stable ionic liquid-based colloidal dispersions can be obtained at room temperature for years, and remain stable at temperatures up to 200 degrees C with concentrations up to 12 vol% (= 30 wt%).