Marangoni-overriding flow in laser-irradiated particle-capped droplets

When a surface tension gradient exists, a Marangoni flow typically occurs from regions of lower to higher surface tension. Here, we report an overriding of this flow in laser-irradiated droplets capped with a jammed particle layer, where particles migrate along the interface toward the apex of reduced surface tension, against the thermal gradient, via a propagating unjamming front. Initial jamming immobilizes light-absorbing particles at the apex, enabling photothermal energy accumulation therein; this removes the central particles and triggers local, intense evaporation that flattens the apex. This flattening steepens the curvature gradient across the unjammed region, amplifying the centripetal Laplace pressure gradient, which dominates over the opposing hydrostatic and Marangoni stresses to drive centripetal transport-a regime we term Marangoni-overriding flow. This flow continually delivers fresh particles to the apex, sustaining the localized energy absorption and thus the intense evaporation that maintains a nonequilibrium curvature field, thereby keeping the Laplace pressure gradient active. This flow regime recasts interfacial jamming as an active control mechanism and, with its tunability via laser power, droplet size, and fluid viscosity, opens avenues for optofluidics, targeted delivery, and nonequilibrium interface engineering.