# Multi-scale control of active emulsion dynamics

## TL;DR

This study demonstrates how localized active behavior in a multi-component 2D film can control energy transfer and flow dynamics, enabling manipulation of active flows through external doping and activity patterns.

## Contribution

It introduces a method to control energy transfer scales in active emulsions by confining activity and modulating activity patterns, without turbulence.

## Key findings

- Active stress induces multi-scale dynamics without turbulence.
- Increased active doping reduces drag via elastic and dissipative stress competition.
- Non-homogeneous activity patterns cause localized flow responses and slip length modulation.

## Abstract

We numerically study the energy transfer in a multi-component $2d$ film, made of an active polar gel and a passive isotropic fluid in presence of surfactant favoring emulsification. We show that by confining the active behavior into the localized component, the typical scale where chemical energy is transformed in mechanical energy can be substantially controlled. Quantitative analysis of kinetic energy spectra and fluxes shows the presence of a multi-scale dynamics due to the existence of a flux induced by the active stress only, without the presence of a turbulent cascade. An increase in the intensity of active doping induces drag reduction due to the competition of elastic and dissipative stresses against active forces. Furthermore we show that a non-homogeneous activity pattern induces localized response, including a modulation of the slip length, opening the way toward the control of active flows by external doping.