Deforming Active Droplets in Viscoelastic Media

TL;DR

This study investigates how active droplets deform and move in viscoelastic fluids, revealing complex behaviors like steady shapes and oscillations, with theoretical predictions aligning with experimental observations.

Contribution

It introduces a novel experimental system for active droplets in viscoelastic media and provides a theoretical framework to predict their shapes and dynamics.

Findings

Droplets exhibit steady deformed shapes at moderate Deborah numbers.

Time-periodic deformations and oscillatory swimming modes occur at higher Deborah numbers.

Theoretical analysis accurately predicts droplet shapes based on normal stress balance.

Abstract

To mimic the motion of biological swimmers in bodily fluids, a novel experimental system of micellar solubilization driven active droplets in a visco-elastic polymeric solution is presented. The visco-elastic nature of the medium, characterized by the Deborah number (De), is tuned by varying the surfactant (fuel) and polymer concentration in the ambient medium. At moderate De, the droplet exhibits a steady deformed shape, markedly different from the spherical shape observed in Newtonian media. A theoretical analysis based on the normal stress balance at the interface is shown to accurately predict the droplet shape. With a further increase in De, time-periodic deformations accompanied by oscillatory transitions in swimming modes are observed. The study unveils the rich complexity in the motion of active droplets in viscoelastic fluids, which has been hitherto unexplored.