Alternative mechanism for coffee-ring deposition based on active role of free surface

Abstract

When a colloidal sessile droplet dries on a substrate, the particles suspended in it usually deposit in a ring-like pattern. This phenomenon is commonly referred to as the "coffee-ring" effect. One paradigm for why this occurs is as a consequence of the solutes being transported towards the pinned contact line by the flow inside the drop, which is induced by surface evaporation. From this perspective, the role of the liquid-gas interface in shaping the deposition pattern is somewhat minimized. Here, we propose an alternative mechanism for the coffee-ring deposition. It is based on the bulk flow within the drop transporting particles to the interface where they are captured by the receding free surface and subsequently transported along the interface until they are deposited near the contact line. That the interface captures the solutes as the evaporation proceeds is supported by a Lagrangian tracing of particles advected by the flow field within the droplet. We model the interfacial adsorption and transport of particles as a one-dimensional advection-generation process in toroidal coordinates and show that the theory reproduces ring-shaped depositions. Using this model, deposition patterns on both hydrophilic and hydrophobic surfaces are examined in which the evaporation is modeled as being either diffusive or uniform over the surface.

References in corpus (10)

• Evaporative Deposition Patterns Revisited: Spatial Dimensions of the Deposit
• Order-to-disorder transition in ring-shaped colloidal stains
• Controlled uniform coating from the interplay of Marangoni flows and surface-adsorbed macromolecules
• Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study
• Effects of Particle Shape on Growth Dynamics at Edges of Evaporating Colloidal Drops
• Analytical solution of Stokes flow inside an evaporating sessile drop: Spherical and cylindrical cap shapes
• Capillary flow in an evaporating sessile drop
• Analytical solution for inviscid flow inside an evaporating sessile drop
• Molecular dynamics simulations of the evaporation of particle-laden droplets
• Homogeneous deposition of particles by absorption on hydrogels

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• Applying Droplets and Films in Evaporative Lithography
• The nascent coffee ring: how solute diffusion counters advection
• Contact-line deposits from multiple evaporating droplets
• Particle monolayer assembly in evaporating salty colloidal droplets
• The nascent coffee ring with arbitrary droplet contact set: an asymptotic analysis
• Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops
• Compound redistribution due to droplet evaporation on a thin polymeric film: theory
• Simultaneous evaporation and imbibition of a droplet on a flooded porous substrate
• Uniform coating of self-assembled non-iridescent colloidal nanostructures using Marangoni effects and polymers