Soft channel formation and symmetry breaking in exotic active emulsions

TL;DR

This study uses simulations to explore how active emulsions with a passive fluid and active gel form various structures under different shear and activity levels, revealing new morphologies and rheological behaviors.

Contribution

It introduces a detailed simulation analysis of active emulsion morphologies, including soft channel formation and symmetry breaking, under varying activity and shear conditions.

Findings

Three distinct morphologies identified: lamellar, asymmetric, and soft channel states.

Active forcing increases the effective shear viscosity, causing fluid thickening.

Symmetry breaking and banding occur at intermediate activity and shear levels.

Abstract

We use computer simulations to study the morphology and rheological properties of a bidimensional emulsion resulting from a mixture of a passive isotropic fluid and an active contractile polar gel, in the presence of a surfactant that favours the emulsification of the two phases. By varying the intensity of the contractile activity and of an externally imposed shear flow, we find three possible morphologies. For low shear rates, a simple lamellar state is obtained. For intermediate activity and shear rate, an asymmetric state emerges, which is characterized by shear and concentration banding at the polar/isotropic interface. A further increment in the active forcing leads to the self-assembly of a soft channel where an isotropic fluid flows between two layers of active material. We characterize the stability of this state by performing a dynamical test varying the intensity of the active forcing and shear rate. Finally, we address the rheological properties of the system by measuring the effective shear viscosity, finding that this increases as active forcing is increased, so that the fluid thickens with activity.