Effects of Matrix Viscoelasticity on Rheology of Dilute and Semi-Dilute Suspensions of Non Brownian Rigid Spheres

摘要

The rheology of non-Brownian, inertialess rigid spheres suspended in viscoelastic fluids was investigated in the dilute and semi-dilute regimes (volume fractions up to 10%), where interparticle interactions become increasingly relevant. PMMA spherical particles were suspended in viscoelastic Polydimethylsiloxanes (PDMS). A Newtonian fluid (Polyisobutilene, PIB) was also used as a reference system. As expected, both the viscosity and the viscoelastic moduli increased with increasing solid volume fraction. The rheological parameters showed a simple scaling behaviour when their normalized values (with respect to the pure fluid) were considered. Viscosity and moduli were found to be independent upon shear rate and frequency, respectively. Following Batchelor's approach for non-dilute Newtonian suspensions, a second order polynomial dependency for the rheological properties was assumed. While the Newtonian reference fluid was found to obey well Batchelor's theoretical predictions, the viscoelastic suspensions showed more pronounced deviations from the linear dilute behavior, resulting in a second order polynomial coefficient substantially larger than that predicted by Batchelor for Newtonian systems. It was also found that the same concentration dependence was followed by both elastic and loss modulus.