(367d) Rheology and Complex Flow of a Concentrated Bimodal Suspension

In this work, the rheology of a bimodal suspension of neutrally buoyant, noncolloidal spheres in a viscous, Newtonian liquid is investigated. The smaller particles are alginate gel microbeads, which are deformable and porous, and the larger particles are rigid PMMA spheres with a diameter approximately three times greater. Preliminary results at a total particle volume fraction of 0.5  show that the viscosity increases and becomes increasingly shear thinning as the fraction of larger, rigid particles increases. Comparisons to monomodal suspensions of either particle type will be presented. Rheological phenomena can also be related to nuclear magnetic resonance imaging (NMRI) observations of the suspensions flowing through an abrupt, axisymmetric 1:4 contraction-expansion. At high fractions of large particles, the small particle fraction appears to act as a lubricant near the wall of the contraction-expansion and promote plug flow of the large particle fraction, which suggests the potential of small particle additives for extrusion processing of composites.