Minimal size of coffee ring structure

Xiaoying Shen, Chih Ming Ho, Tak Sing Wong

Research output: Contribution to journalArticle

211 Scopus citations

Abstract

A macroscopic evaporating water droplet with suspended particles on a solid surface will form a ring-like structure at the pinned contact line due to induced capillary flow. As the droplet size shrinks, the competition between the time scales of the liquid evaporation and the particle movement may influence the resulting ring formation. When the liquid evaporates much faster than the particle movement, coffee ring formation may cease. Here, we experimentally show that there exists a lower limit of droplet size, Dc, for the successful formation of a coffee ring structure. When the particle concentration is above a threshold value, Dc can be estimated by considering the collective effects of the liquid evaporation and the particle diffusive motion within the droplet. For suspended particles of size ∼100 nm, the minimum diameter of the coffee ring structure is found to be ∼10 μm.

Original languageEnglish (US)
Pages (from-to)5269-5274
Number of pages6
JournalJournal of Physical Chemistry B
Volume114
Issue number16
DOIs
StatePublished - Apr 29 2010

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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