Non-Equilibrium Fluidization of Dense Active Suspension

TL;DR

This paper explores how dense suspensions of swimming bacteria exhibit non-equilibrium behaviors, including reduced viscosity and critical jamming, driven by bacterial activity in a nutrient-exchange environment.

Contribution

It reveals the non-equilibrium fluidization phenomena and power-law rheology in dense active bacterial suspensions, highlighting activity-induced critical jamming.

Findings

Viscosity decreases significantly in active suspensions.

Dynamic heterogeneity and non-Newtonian viscosity disappear with activity.

Complex shear modulus follows a power-law with exponent 1/2.

Abstract

We investigate dense suspensions of swimming bacteria prepared in a nutrient-exchange chamber. Near the pellet concentration, nonthermal fluctuations showed notable agreement between self and collective behaviors, a phenomenon not previously observed at equilibrium. The viscosity of active suspensions dramatically decreased compared to their inactive counterparts, where glassy features, such as non-Newtonian viscosity and dynamic heterogeneity, disappeared. Instead, the complex shear modulus showed a power-law rheology,$G^*(\omega)\propto\left(-i\omega\right)^\frac{1}{2}$, indicating the role of bacterial activity in driving the system towards a critical jamming state.