Steric repulsion as a way to achieve the required stability for the preparation of ionic liquid-based ferrofluids

• Published in: Journal of colloid and interface science 2011-05, Vol.357 (1), p.252-254
• Main Authors: RODRIGUEZ-ARCO, Laura, LOPEZ-LOPEZ, Modesto T, GONZALEZ-CABALLERO, Fernando, DURAN, Juan D. G
• Format: Article
• Language: English
• Subjects: centrifugation; Chemistry; Colloidal state and disperse state; Double layer; Exact sciences and technology; Ferrofluid; Ferrofluids; General and physical chemistry; Ionic liquid; ionic liquids; Magnetic fields; Magnetic materials; Magnetite; Nanoparticle; Nanoparticles; Oleic acid; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Sedimentation; Stability; Viscoelasticity; Yield stress
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.01.083

Magnetite nanoparticles coated with a double layer of oleic acid dispersed in an ionic liquid ([EMIM][EtSO 4]) give rise, by steric repulsion, to a true ferrofluid: with long-life colloidal stability. [Display omitted] ► Suspensions of magnetic nanoparticles in ionic liquids are prepared. ► Bare nanoparticles irreversibly aggregate when dispersed in the ionic liquid. ► Electrostatic repulsion in ionic liquids seems to be screened. ► Coverage with compatible surfactant layers is required to obtain a stable ferrofluid. ► Stability in these ferrofluids is achieved by a steric repulsion mechanism. With this work we would like to emphasize the necessity of steric repulsion to stabilize novel ionic liquid-based ferrofluids. For this purpose, we prepared a suspension of magnetite nanoparticles coated with a double layer of oleic acid, dispersed in 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM][EtSO 4]). For comparison, a suspension of bare magnetite nanoparticles in [EMIM][EtSO 4] was also prepared. The stability of these suspensions was checked by magnetic sedimentation and centrifugation processes. Furthermore, their yield stress was measured as a function of the applied magnetic field, which gave additional information on their stability. The results of these experiments showed that the suspension of bare nanoparticles was rather unstable, whereas the suspension of double layer coated nanoparticles gave rise to a true (stable) ferrofluid.