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Monolith formation and ring-stain suppression in low-pressure evaporation of poly(ethylene oxide) droplets

Research output: Contribution to journalArticle

  • Kyle A. Baldwin
  • Samuel Roest
  • David J. Fairhurst
  • Khellil Sefiane
  • Martin E. R. Shanahan

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Original languageEnglish
Pages (from-to)321-329
Number of pages9
JournalJournal of Fluid Mechanics
Volume695
DOIs
Publication statusPublished - Mar 2012

Abstract

When droplets of dilute suspensions are left to evaporate the final dry residue is typically the familiar coffee-ring stain, with nearly all material deposited at the initial triple line (Deegan et al., Nature, vol. 389, 1997, pp. 827-829). However, aqueous poly(ethylene oxide) (PEO) droplets only form coffee-ring stains for a very narrow range of the experimental parameters molecular weight, concentration and drying rate. Instead, over a wide range of values they form either a flat disk or a very distinctive tall central monolith via a four-stage deposition process which includes a remarkable bootstrap-building step. To predict which deposit will form, we present a quantitative model comparing the effects of advective build-up at the triple line to diffusive flux and use this to calculate a dimensionless number Χ. By experimentally varying concentration and flux (using a low-pressure drying chamber), the prediction is tested over nearly two orders of magnitude in both variables and shown to be in good agreement with the boundary between disks and monoliths at χ≈1.6.

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