  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.
