Rheology of dilute and semi-dilute non-Brownian suspensions made of irregular porous particles in a Newtonian fluid

Hypothesis: The porosity affects the rheological response of porous particle suspensions.

Experiments: Non-Brownian suspensions of porous particles immersed in a Newtonian Polyisobutene are investigated. Three different particles, with different porosity, pore structure and similar size, and non-porous irregular particles are used. The steady state and dynamic response of the suspensions are analyzed at several volume fractions.

Findings: The behavior of the three porous particle suspensions is unique if the particle effective volume fraction, accounting for the polymer adsorbed into the particles, is considered. These suspensions are Newtonian until a critical volume fraction, beyond which they are shear thinning and exhibit a yield stress. Their rheological response differs from that of suspensions made of non-porous irregular particles as: (a) their critical volume fraction is much smaller than that of the irregular particle suspensions; (b) their viscoelastic spectra are different suggesting a denser and stronger percolated microstructure after a slow preshear. These results can be understood by considering the reduction of lubrication force induced by the porosity via two mechanisms: Darcyan flow through the porosity and propagation of the interparticle shear flow within the porosity. The first dominates at low shear rates, when the percolated microstructure is generated, the second prevails at high shear rates, where the particle clusters are disaggregated.