DOI: 10.1140/epje/i2002-10066-4
Viscosity minimum in bimodal concentrated suspensions under shear
A. Núñez, R. Darias, R. Pinto, R. Paredes V. and E. MedinaLaboratorio de Física Estadística de Sistemas Desordenados, Centro de Física, IVIC, Apartado 21827, Caracas 1020A, Venezuela ernesto@pion.ivic.ve
(Received 28 June 2002 / Published online: 14 January 2003)
Abstract
We study a model of concentrated suspensions under shear in two
dimensions. Interactions between suspended particles are dominated by
direct-contact viscoelastic forces and the particles are neutrally
bouyant. The bimodal suspensions consist of a variable proportion
between large and small droplets, with a fixed global suspended
fraction. Going beyond the assumptions of the classical theory of
Farris (R.J. Farris, Trans. Soc. Rheol. 12, 281 (1968)),
we discuss a shear viscosity minimum, as a
function of the small-to-large-particle ratio, in shear geometries
imposed by external body forces and boundaries. Within a linear-response
scheme, we find the dependence of the viscosity minimum on
the imposed shear and the microscopic drop friction parameters. We
also discuss the viscosity minimum under dynamically imposed shear
applied by boundaries. We find a reduction of macroscopic viscosity
with the increase of the microscopic friction parameters that is
understood using a simple two-drop model. Our simulation results are
qualitatively consistent with recent experiments in concentrated
bimodal emulsions with a highly viscous or rigid suspended component.
83.80.Hj - Suspensions, dispersions, pastes, slurries, colloids.
02.70.Ns - Molecular dynamics and particle methods.
83.80.Fg - Granular solids.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
