Influence of bubble lifetime on the drying of catalytically active sessile droplets

Abstract When colloidal droplets evaporate, suspended particles are redistributed by a competition between evaporation-driven capillary advection, interfacial Marangoni stresses and particle mobility, leading to diverse deposition patterns relevant to coating and self-assembly. While these mechanisms are well understood for passive suspensions, their interplay in chemically active colloidal systems remains less explored. Here, we investigate the drying dynamics of aqueous droplets containing catalytic polystyrene-platinum (PS-Pt) Janus particles in the presence of hydrogen peroxide (H 2 O 2 ) fuel. H 2 O 2 undergoes catalytic decomposition at the Pt hemisphere, resulting in the generation of oxygen (O 2 ). By systematically varying H 2 O 2 concentration, surface wettability and open versus confined drying conditions, we identify distinct transport regimes governed by the interplay between capillary flow and an inward flow driven by activity-induced surface tension gradients. While time-resolved contact angle measurements reveal substrate-dependent evaporation modes, increase in catalytic activity promotes O 2 bubble generation that locally reverses or disrupts outward particle transport. Closed drying conditions further modify evaporation rates and prolong bubble lifetimes, leading to transitions from peripheral accumulation to spatially uniform or centrally concentrated deposits. Bubble lifetime, controlled here by tuning substrate wettability and H 2 O 2 concentration, therefore emerges as the dominant mechanism governing the dried morphologies of catalytically active Janus particle droplets.