Irreversibility and rate dependence in sheared adhesive suspensions

Abstract

Recent experiments report that slowly-sheared noncolloidal particle suspensions can exhibit unexpected rate(ω)-dependent complex viscosities in oscillatory shear, despite a constant relative viscosity in steady shear. Using a minimal hydrodynamic model, we show that a weak interparticle attraction reproduces this behavior. At volume fractions φ = 20 ∼ 50%, the complex viscosities in both experiments and simulations display power-law reductions in shear, with a φ-dependent exponent maximum at φ = 40%, resulting from the interplay between hydrodynamic, collision and adhesive interactions. Furthermore, this rate dependence is accompanied by diverging particle diffusivities and pronounced cluster formations even at small oscillation amplitudes γ0. Previous studies established that suspensions transition from reversible absorbing states to irreversible diffusing states when γ0 exceeds a φ-dependent critical value γ c 0,φ . Here, we show that a second transition to irreversibility occurs below an ω-dependent critical amplitude, γ c 0,ω ≤ γ c 0,φ , in the presence of weak attractions.