Rheology of non-colloidal suspensions with viscoelastic matrices

The rheology of non-colloidal suspensions of spheres in a viscoelastic matrix, including the viscometric, G', G' and uniaxial extensional responses, is explored. Volume fractions of 50% and less were used. By recognizing that filament stretching between beads begins at a distance comparable to the sphere diameter the unexpected large stresses seen in the uniaxial extension experiments can be understood, and a model is presented. In the experiments there is little variation of the dimensionless elongational stresses with the volume fraction φ. For a volume fraction of 50% the behaviour was different from the other concentrations. An essential finding is that a single-mode model of the Oldroyd-B type is not able to describe the elongational experiments at all-at least two modes are needed. There is clearly a difference between behaviour in elongation and in shear with regards to the action of interparticle friction. With negligible rotation of the particles in elongation the kind of vigorous interparticle rubbing possible in shear does not happen.