Dynamic characterization of extremely bidisperse magnetorheological fluids

• Published in: Journal of colloid and interface science Vol. 377; no. 1; pp. 153 - 159
• Main Authors: Iglesias, G.R., López-López, M.T., Durán, J.D.G., González-Caballero, F., Delgado, A.V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-07-2012; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; Ferrofluid; General and physical chemistry; hardness; Iron; Iron particles; Lubricant rheology; Magnetic fields; Magnetic nanoparticles; magnetite; Magnetorheological fluids; Nanoparticles; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Redispersibility; Sediments; Stability; viscosity; Volume fraction; Lubricant rheology; Ferrofluid; Redispersibility; Stability; Iron particles; Magnetic nanoparticles; Magnetorheological fluids; Viscosity; Iron oxide; Volume fraction; Force; Nanoparticle; Stabilization; Iron; Solid; Characterization; Design; Particle; Magnetite; Dynamics; Microparticle; Magnetic field; Attraction; External field; Rheology; Fluid; Suspension; Transition metal; Hardness; Sediments; Steady state; Sedimentation; Dispersion; Lubricant; Liquid; Penetration
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2012.03.077

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► The dynamic behavior of bimodal magnetorheological fluids is studied. ► Their settling rate is highly modified by the addition of small amounts of nanomagnetite. ► A standard penetration needle is used for the prediction of redispersibility. ► A hard sediment is absent if magnetite is added. ► Magnetorheology experiments confirm that the mixed fluids have excellent performance.
In this work, we investigate the stability and redispersibility of magnetorheological fluids (MRFs). These are disperse systems where the solid is constituted by ferro- or ferri-magnetic microparticles. Upon the application of external magnetic field, they experience rapid and reversible increases in yield stress and viscosity. The problem considered here is first of all the determination of their stability against sedimentation, an essential issue in their practical application. Although this problem is typically faced through the addition of thixotropic agents to the liquid medium, in this work, we propose the investigation of the effect of magnetic nanoparticles addition, so that the dispersion medium is in reality a ferrofluid. It is found that a volume fraction of nanoparticles not higher than 3% is enough to provide a long-lasting stabilization to MRFs containing above 30% iron microparticles. In the, in fact unavoidable, event of settling, the important point is the ease of redispersion of the sediment. This is indirectly evaluated in the present investigation by measuring the penetration force in the suspension, using a standard hardness needle. Again, it is found that the nanoparticles addition produces soft sediments by avoiding short-range attractions between the large iron particles. Finally, the performance of the designed MRFs is evaluated by obtaining their steady-state rheograms for different volume fractions of magnetite and different magnetic field strengths. The yield stress is found to be strongly field-dependent, and it can achieve the high values expected in standard magnetorheological fluids but with improved stability and redispersibility.