Influence of Bubble Lifetime on the Drying of Catalytically Active Sessile Droplets

TL;DR

This study explores how bubble lifetime influences evaporation and particle deposition patterns in catalytically active Janus droplet systems, revealing bubble-induced Marangoni flow as a key factor.

Contribution

It demonstrates the role of catalytic bubble dynamics in controlling drying behavior and deposit morphology in active colloidal droplets.

Findings

Bubble generation disrupts outward particle transport.

Open vs. closed conditions affect evaporation and deposit patterns.

Substrate wettability influences bubble residence time and flow regimes.

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 droplets containing catalytic polystyrene-platinum (PS-Pt) Janus particles in the presence of hydrogen peroxide (H2O2) fuel. H2O2 undergoes catalytic decomposition at the Pt hemisphere, resulting in the formation of oxygen (O2). By systematically varying H2O2 concentration, surface wettability and open versus confined drying conditions, we identify distinct transport regimes governed by the relative magnitudes of capillary flow and gas bubble-induced Marangoni convection. While time-resolved contact-angle measurements reveal substrate-dependent evaporation modes, an increase in catalytic activity promotes O2 bubble generation that locally reverses or disrupts outward particle transport. Closed drying conditions further modify evaporation rates and prolong bubble residence times, leading to transitions from peripheral accumulation to spatially uniform or centrally concentrated deposits. Bubble-induced Marangoni flow, controlled here by tuning substrate wettability and environmental conditions, therefore emerges as the dominant mechanism governing the evaporation dynamics and dried morphologies of catalytically active Janus particle droplets.