Irreversibility and rate dependence in sheared adhesive suspensions

TL;DR

This study demonstrates that weak interparticle attractions in sheared adhesive suspensions cause rate-dependent complex viscosities, particle clustering, and multiple irreversibility transitions, revealing complex interplay between hydrodynamics, collisions, and adhesion.

Contribution

It introduces a minimal hydrodynamic model showing how weak attractions induce rate dependence and multiple irreversibility transitions in sheared suspensions.

Findings

Complex viscosities exhibit power-law shear rate dependence.

Particle diffusivities diverge with increasing oscillation amplitude.

A second irreversibility transition occurs below the known critical amplitude.

Abstract

Recent experiments report that slowly-sheared noncolloidal particle suspensions can exhibit unexpected rate($\omega$)-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 $\phi=20\sim50$%, the complex viscosities in both experiments and simulations display power-law reductions in shear, with a $\phi$-dependent exponent maximum at $\phi=40$%, 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 $\gamma_0$. Previous studies established that suspensions transition from reversible absorbing states to irreversible diffusing states when $\gamma_0$ exceeds a $\phi$-dependent critical value $\gamma_{0,\phi}^c$. Here, we show that a second transition to irreversibility occurs below an $\omega$-dependent critical amplitude, $\gamma_{0,\omega}^c \leq \gamma_{0,\phi}^c$, in the presence of weak attractions.