(526h) Nanomotor-Enhanced Diffusion Transport in Porous Media

Self-propelled motion of artificial micro- and nanomotors is broadly studied due to fundamental interest in emergent behaviors as well as potential applications in areas including biomedical and environmental science. Active colloids are expected to perform tasks under complex, species-rich and interface-rich environments. Interactions between active matter and passive moieties have been scrutinized in bulk solution system. However, the influence of active motion on the transport of passive particles in a confined and interconnected environment remains unclear. Here, we applied 3D single-particle tracking to investigate the impact of nanomotors (Pt-coated polystyrene Janus particles) on passive particles confined in a porous structure (a silica inverse opal). Interestingly, we observed substantially enhanced transport of passive particles in the presence of H₂O₂-powered nanomotors in the interface-confined environment, even at very low concentration of the active particles. For example, the passive particles escaped from porous cavities 2x faster in the presence of nanomotors; in bulk solution, however, the same concentration of nanomotors had no measurable effect on the motion of passive Brownian particles. Previous research found that the rapid transport of active particles in confined environments is due in part to the effective elimination of electrostatic barriers. We speculate that the short-range convective circulation associated with self-propulsion is amplified and extended in a confined and interconnected environment, resulting in the elimination of energy barriers to surrounding passive particles, thus improving their transport efficiency. This finding indicates a potential role of active particles as remobilizers, to enhance the transport of surrounding species and even to degrade the aggregates, unblocking porous structures. In the context of pore-constricted trapping in fouling processes, active particles may provide an intriguing approach to reduce or reverse fouling for filtration membranes.