Impact of particle stiffness on shear-thinning of non-Brownian suspensions

Abstract

We attempt to identify the impact of particle stiffness on the shear-thinning behavior exhibited by frictional and adhesive non-Brownian suspensions. To this aim, we compare the rheological behavior of three suspensions whose particles have different Young's moduli.The stiffest particles are Soda-lime glass beads with a Young modulus of 70 GPa. The two other kinds of particles are made of polydimethylsiloxane and have been manufactured using a homemade millifluidic device that allowed us to produce batches of sparsely polydisperse particles with tunable Young modulus: 1.8 MPa for the softest ones and 15 MPa for the stiffest. We show that the observed shear-thinning is mainly caused by the presence of adhesive forces between particles. For each of the three suspensions, the shear-thinning behavior is described by the variation of the jamming volume fraction, φ m , with stress, σ , and the results are interpreted in the light of the model proposed by [Richards et al., J. Rheol. 64(2), 405-412 (2020)]. We show that the magnitude of variation of φ m with σ is greater the lower the particle stiffness. More precisely, in the adhesive regime, decreasing the particle stiffness leads to a significant decrease in the value of the jamming fraction while, as predicted by the JKR theory, the characteristic adhesion stress, σ a , does not vary with stiffness. We finally show that, for stresses much higher than σ a , the suspensions behave like usual frictional suspensions with a viscosity controlled by both the particle volume fraction and the value of the interparticle friction coefficient.

A particulate blood analogue based on artificial viscoelastic blood plasma and RBC-like microparticles at a concentration matching the human haematocrit

“…The mechanism responsible for the shear-thinning behaviour has motivated many studies in the last few decades on several systems as Brownian colloidal suspensions and non-Brownian suspensions, and for rigid and less rigid microparticles. The shear-thinning behaviour of our suspensions (in the limit of non-Brownian suspensions) could be mainly caused by the presence of adhesive forces between particles, as reported by Gilbert et al 45 in their study on PDMS suspensions. When these adhesive forces are presented, the shear-thinning behaviour appears because of the formation of agglomerates that break down when the deformation is increased, leading to a reduction of these structures into units and thus decreasing the viscosity with the shear rate, 46 as in the case of blood.…”

“…The capillary number Ca can be written as follows:where σ is the shear stress and E the elastic modulus of the particles. 49…”

“…where s is the shear stress and E the elastic modulus of the particles. 49 Under flow, high values of Ca mean that particles are more sensitive to the variation of the shear rate leading to a change in their shape. 50 The highest Ca corresponds to samples with particles with a mixing PDMS ratio of 60 : 1 (Ca 60:1 4 Ca 45:1 4 Ca 30:1 ).…”

The Role of Structure in Polymer Rheology: Review

“…Additional rheological effects arise if dispersed particles are soft and can be deformed in the flow. According to this model and experimental data obtained for polymeric particles, this structure peculiarity is directly linked with shear thinning of a medium [ 75 , 76 ].…”

Microscopically grounded constitutive model for dense suspensions of soft particles below jamming

“…The value of φ J depends on geometrical aspects like particle shape [4], or the nature of constraints to motion created by interactions, such as friction or adhesion [6]. Crucially however, it does not depend on the softness of the particles per se, insofar as softness is not affecting friction or adhesion [7].…”