Magnetorheology in strongly structured media

O. Volkova¹ - E. Lemaire¹ - G. Bossis¹ - V. Bashtovoi² - N. Matoussevitch² - A. Reks²

¹ Laboratoire de Physique de la Matiere Condensee, Universite de Nice, Parc Valrose, 06108 Nice, France
² Belorusian State Academy, Laborathory of Thermomechanics of Magnetic Fluids, Minsk, 220027, Bielorussia

Abstract
We present experimental results on the viscosity and initial permeability of magnetic suspensions made of silica particles (diameter 40-50 mm) suspended in a ferrofluid. The rheograms are quite well represented by a Casson law with a yield stress which scales as the permeability of the ferrofluid multiplied by the square of the effective field in the suspension. We present an analytical model based on a representation of the structure as an assembly of cylinders which allows to predict the yield stress of these suspensions without any adaptable parameters. This model is shown to be in good agreement with a numerical model developed previously and based on a chain structure of the silica particles. The order of magnitude of the experimental yield stress is well predicted by these models except at high volume fraction where the discrepancy increases. On the other hand the dependence of the permeability on the volume fraction is quite well represented by simple average field models. Tabl. 3, figs 2, refs 12.