arXiv subjects

Meneka Banik

Publications and source records attributed to Meneka Banik.

3 recordsLinked to original sources

arXiv2026

From Coffee Rings to Self-Driven Assembly: Active Matter Enabled Design of Drying Droplets

Evaporating colloidal droplets have long been used as model systems to understand capillarity, interfacial transport, and particle assembly, most prominently through the coffee ring effect. In classical descriptions, suspended particles are treated as passive tracers carried by evaporation-driven capillary flow, with additional influence from Marangoni stresses, wettability, and contact line pinning. More recent studies, however, show that this picture changes significantly when the particles themselves are active. Systems containing motile microorganisms, chemically active colloids, or externally driven particles can continuously inject energy or generate gradients within the droplet, leading to self-driven flows, modified interfacial stresses, and dynamic contact line behavior. In this Perspective, we bring together these developments, identify the key mechanisms governing active droplets, highlight the role of bubble-mediated flows, and outline strategies for controlled deposition and functional interface design.

cond-mat.soft↗

arXiv2026

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

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.

cond-mat.soft↗

arXiv2025

Bubble-Driven Flow Transitions in Evaporating Active Droplets on Structured Surfaces

The evaporation of particle-laden droplets on engineered surfaces underpins a wide range of technologies, from printed electronics to biosensing. While the influence of substrate topography on passive particle deposition is well established, the combined effects of active matter dynamics, catalytic gas generation, and surface structuring remain unexplored. Here, we investigate the drying of aqueous droplets containing Janus particles (polystyrene-platinum, PS-Pt) on topographically patterned substrates in the presence of hydrogen peroxide (H2O2) fuel. The catalytic decomposition of H2O2 produces oxygen bubbles within the droplet, introducing strong, transient hydrodynamic perturbations that compete with evaporation driven capillary flows and contact line interactions. We show that bubble activity alters particle transport, leading to distinct and tunable final morphologies not achievable with passive suspensions. This study demonstrates how bubble-induced flow coupled with substrate topography determines deposition patterns during droplet evaporation. Our findings open a route to harnessing active matter and reaction driven flows for directed particle assembly.

cond-mat.soft↗