# Swimming to Stability: Structural and Dynamical Control via Active Doping

## TL;DR

This study demonstrates how active particles within a colloidal gel can dynamically alter its free energy landscape, enabling control over its structure and phase behavior through tunable active forces and solvent viscosity.

## Contribution

It introduces a novel approach of using active particles to modulate the dynamical free energy landscape and phase behavior of soft materials.

## Key findings

- Active particles can bypass kinetic barriers in gels.
- Tuning active particle properties influences phase transitions.
- Solvent viscosity affects the material's state.

## Abstract

External fields can decidedly alter the free energy landscape of soft materials and can be exploited as a powerful tool for the assembly of targeted nanostructures and colloidal materials. Here, we use computer simulations to demonstrate that nonequilibrium internal fields or forces -- forces that are generated by driven components within a system -- in the form of active particles can precisely modulate the dynamical free energy landscape of a model soft material, a colloidal gel. Embedding a small fraction of active particles within a gel can provide a unique pathway for the dynamically frustrated network to circumvent the kinetic barriers associated with reaching a lower free energy state through thermal fluctuations alone. Moreover, by carefully tuning the active particle properties (the propulsive swim force and persistence length) in comparison to those of the gel, the active particles may induce depletion-like forces between the constituent particles of the gel despite there being no geometric size asymmetry between the particles. These resulting forces can rapidly push the system toward disparate regions of phase space. Intriguingly, the state of the material can be altered by tuning macroscopic transport properties such as the solvent viscosity. Our findings highlight the potential wide-ranging structural and kinetic control facilitated by varying the dynamical properties of a remarkably small fraction of driven particles embedded in a host material.