  The growing interest in the non-equilibrium assembly of colloidal particles
in active liquids is driven by the motivation to create novel structures
endowed with tunable properties unattainable within the confines of equilibrium
systems. Here, we present an experimental investigation of the structural
features of colloidal assemblies in active liquids of chiral E. coli. The
colloidal particles form dynamic clusters due to the effective interaction
mediated by active media. The activity and chirality of the swimmers strongly
influence the dynamics and local ordering of colloidal particles, resulting in
clusters with persistent rotation, whose structure differs significantly from
those in equilibrium systems with attractive interactions, such as
colloid-polymer mixtures. The colloid-bacteria mixture displays several
hallmark features of a percolation transition at a critical density, where the
clusters span the system size. However, a closer examination of the critical
exponents associated with cluster size distribution, average cluster size, and
correlation length in the vicinity of the critical density suggest strong
deviations from the prediction of the standard continuum percolation model.
Therefore, our experiments reveal a richer phase behavior of colloidal
assemblies in active liquids.
