Surface-modified cerium oxide nanoparticles synthesized continuously in supercritical methanol: Study of dispersion stability in ethylene glycol medium

Dispersion stability of surface-modified cerium oxide (CeO₂) nanoparticles in ethylene glycol is examined and the experimental stability results are compared with an extended DLVO model consisting of electrostatic, van der Waals, and hydrophobic/hydrophilic interactions. Unmodified, decanoic acid-modified and oleic acid-modified CeO₂ nanoparticles are synthesized continuously in supercritical methanol (scMeOH). The surface charge of the surface-modified CeO₂ particles changes from positive to negative with an increment in the medium pH while the surface charge of the unmodified CeO₂ particle does not change with varying pH. Long-term dispersion stability test (up to 100 days) shows that the oleic acid-modified nanoparticle with a concentration of 0.3M retains most stable dispersion in ethylene glycol. The unmodified and decanoic acid-modified nanoparticles with a concentration of 0.03M precipitate within 7-15 days. In contrast, initial short-term stability evolution reveals different stability behavior compared to the long-term stability. The unmodified and the decanoic acid-modified nanoparticles with a concentration of 0.03M were less attractive than the oleic acid-modified nanoparticle with 0.3M. The experimental short-term stability data is in good agreement with the computational results of energy profiles for the CeO₂ nanoparticle suspension.