Electrorheologial properties of hematite/silicone oil suspensions under DC fields |
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| Institution: | 1. Department of Applied Physics, Faculty of Science, University of Granada, 18071 Granada, Spain;2. Instituto de Investigaciones Eléctricas, Calle Reforma No. 113, Colonia Palmira, 62490 Cuernavaca, Morelos, México;1. Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India;2. TATA Global R&D Division, India;1. Bioprocessing and Biodetection Lab (BBL), Department of Food Science, Technology and Engineering, University of Tehran, Karaj, Iran;2. FRCFT, School of Biosystems and Food Engineering, Agriculture and Food Science Centre, University College Dublin, National University of Ireland, Belfield, Dublin 4, Ireland;1. School of Mathematical Sciences, Huaqiao University, Quanzhou 362021, PR China;2. School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, PR China;3. Beijing Center for Scientific and Computing (BJC-SEC), Beijing University of Technology, Beijing 100124, PR China;4. Department of Physics, Blinn College, Bryan, TX 77805, USA |
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| Abstract: | Electrorheological (ER) fluids composed of α-Fe2O3 (hematite) particles suspended in silicone oil are studied in this work. The rheological response has been characterized as a function of field strength, shear rate and volume fraction. Rheological tests under DC electric fields elucidated the influence of the electric field strength, E, and volume fraction, ϕ, on the field-dependent yield stress, τy. It was found that this quantity scales with E and ϕ with a linear and parabolic dependence, respectively. The viscosities of electrified suspensions were found to increase by several orders of magnitude as compared to the unelectrified suspension at low shear rates, although at high-shear rates hydrodynamic effects become dominant and no effects of the electric field on the viscosity are observed. The work is completed with the analysis of microscopic observations of the structure acquired by the ER fluid upon application of a constant electric field. Electrohydrodynamic convection is found to be the origin of the ER response rather than the commonly admitted particle fibrillation. This fact can provide an explanation to the relationship between yield stress and electric field strength as well as the pattern of periodic structures observed in the measurement geometries. |
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