Contact network structures and rigidity development in two-dimensional bidisperse suspensions

Abstract

Dense non-Brownian suspensions with conservative repulsive forces between the particles are known to exhibit shear thickening, where viscosity increases with applied stress due to a change in the dominant stress mechanism. At low stress, repulsion maintains liquid films that lubricate particle interactions, while higher stress overcomes the repulsion to generate frictional contacts and leads to greater flow resistance. Here, shear-thickened suspensions are studied in stress-controlled simulations incorporating hydrodynamic, electrostatic double-layer repulsion, and frictional forces; two-dimensional monolayers are studied for monodisperse and bidisperse suspensions with size ratios δ=as/al from 1.0 to 4.0, where as and al are the small and large particle radii. Small-particle fractions ζ=ϕs/ϕ=0.25,0.50, and 0.75 are considered. Total area fractions of 0.71≤ϕ≤0.82 are studied, with the larger values at greater size ratios. Flow curves for mono- and bidisperse systems under varying stress are analyzed, along with detailed structural comparisons for different interparticle friction. We examine the approach to shear jamming, through the emergence of rigid local clusters generated by the reduction of degrees of freedom by frictional contacts. The variance of the fraction of particles in rigid clusters increases sharply near the jamming solid fraction, consistent with a second-order phase transition description of the phenomenon. The contact fabric tensor is determined to provide a measure of the structural anisotropy.