Activity removes transport arrest and restores phase separation under geometric confinement

Abstract

Transport and phase separation under geometric confinement play a central role in systems ranging from intracellular organization to porous materials, yet how nonequilibrium activity reshapes collective ordering in constrained environments remains unresolved. Here we demonstrate that confinement alone can qualitatively alter phase separation dynamics, suppressing particle transport, roughening interfaces, and driving an anomalously slow, logarithmic coarsening regime. We further show that introducing activity fundamentally changes this behavior. Self-propulsion restores particle-scale transport, smooths confinement-induced interfacial distortions, and reactivates rapid phase ordering without altering the underlying geometry. By directly relating mean-squared displacement to domain growth kinetics, we show that transport restoration is strongly correlated with, and provides a consistent microscopic explanation for, how activity overcomes geometric barriers and eliminates logarithmic slowdown. Beyond a threshold activity, the system undergoes a transition to fast, power-law coarsening despite persistent confinement. Our results unify activity-enhanced transport in porous media with collective phase separation dynamics and establish a general nonequilibrium principle: activity can reprogram both transport and ordering in geometrically constrained systems. Geometric confinement can trap particles and greatly slow down phase separation in porous materials. Here, the authors show that particle activity restores transport through confined spaces, smooths interfaces, and recovers rapid phase separation even when the confining geometry remains unchanged.