{
  "id": "0906.3878",
  "version": "v2",
  "published": "2009-06-21T17:00:12.000Z",
  "updated": "2016-12-10T04:31:14.000Z",
  "title": "Alternative mechanism for coffee-ring deposition based on active role of free surface",
  "authors": [
    "Saeed Jafari Kang",
    "Vahid Vandadi",
    "James D. Felske",
    "Hassan Masoud"
  ],
  "categories": [
    "physics.flu-dyn",
    "physics.bio-ph"
  ],
  "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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2009-06-21T17:00:12.000Z",
      "title": "Role of the free surface in particle deposition during evaporation of colloidal sessile drops",
      "abstract": "Deposition patterns of particles suspended in evaporating colloidal drops are determined by the flow fields within the drops. Using analytically determined velocities, particle motions are then tracked in a Lagrangian sense. It is found that the majority of particles intersect the free surface as it recedes. Such \"capture\" of particles by the free surface is found to be the major mechanism in establishing the deposition pattern. Patterns are calculated for wetting and non-wetting drops whose contact lines are either pinned or freely moving during evaporation. The distribution of evaporative flux which drives the flows is taken to be that engendered by gas-phase diffusion. The theoretical results are found to agree favorably with available experimental data.",
      "comment": null,
      "journal": null,
      "doi": null,
      "authors": [
        "Hassan Masoud",
        "James D. Felske"
      ]
    },
    {
      "version": "v2",
      "updated": "2016-12-10T04:31:14.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "free surface",
      "colloidal sessile drops",
      "particle deposition",
      "evaporation",
      "colloidal drops"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2009arXiv0906.3878M"
    }
  }
}