N-like rheograms of concentrated suspensions of magnetic particles
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AutorLópez-López, Modesto T.; Rodríguez-Arco, Laura; Zubarev, Andrey; Kuzhir, Pavel; Iskakova, Larisa; González-Caballero, Fernando
The Society of Rheology
MagnetorheologyMagnetic particlesRheogramsConcentrated suspensions
López-López, M.T.; et al. N-like rheograms of concentrated suspensions of magnetic particles. Journal of Rheology, 60(2): 267-274 (2016). [http://hdl.handle.net/10481/40674]
PatrocinadorThis work was supported by project FIS2013-41821-R, MINECO, Spain (Co-funded by ERDF, European Union); by project 3.12.2014/K, Program of Ministry of Science and Education of the Russian Federation; by the Act 211 Government of the Russian Federation, Contract No. 02.A03.21.0006; by grants of RFFI 13-02-91052, 13-01-96047 (Ural), and 14-08-00283; and by project PICS 6102 CNRS/Ural Federal University. L.R.-A acknowledges financial support from University of Granada.
We investigate the rheograms of concentrated suspensions of magnetic particles obtained under imposed shear rate in parallel plate geometry. We show that under magnetic field application the usual trend of the rheogram, i.e., increasing shear stress for the whole range of shear rates, is altered by the appearance of a region in which the shear stress decreases as the shear rate is increased. The existence of this region gives to the rheograms an N-like shape. The two initial regions (preyield regime) of these N-like rheograms present unstable flow, characterized by the oscillation of the shear stress with time for each imposed value of shear rate. We also show that rheograms obtained at different sample thicknesses approximately overlap in the developed flow regime, whereas there is a tendency of the shear stress to increase as the thickness is decreased in the preyield regime. This tendency is likely due to the strengthening of pre-existing particle structures by compression as the gap thickness is decreased. Finally, we analyze the effect of the applied magnetic field strength, H, and demonstrate that the rheograms scale with H^1.5 to a single master curve, for the range of applied magnetic fields under study.