Characteristics of air entrainment during dynamic wetting failure along a planar substrate

E. Vandre, M. S. Carvalho, S. Kumar

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Characteristic substrate speeds and meniscus shapes associated with the onset of air entrainment are studied during dynamic wetting failure along a planar substrate. Using high-speed video, the behaviour of the dynamic contact line (DCL) is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above some critical substrate speed. Meniscus confinement within a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a wide range of liquid viscosities, expanding upon the findings of Vandre, Carvalho & Kumar (J. Fluid Mech., vol. 707, 2012, pp. 496-520). A pressurized liquid reservoir controls the meniscus position within the confinement gap. It is found that liquid pressurization further postpones air entrainment when the meniscus is located near a sharp corner along the stationary plate. Meniscus shapes recorded near the DCL demonstrate that operating conditions influence the size of entrained air films, with smaller films appearing in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, suggesting that strong air stresses near the DCL trigger the onset of air entrainment.

Original languageEnglish (US)
Pages (from-to)119-140
Number of pages22
JournalJournal of Fluid Mechanics
Volume747
Issue number1
DOIs
StatePublished - Apr 10 2014

Keywords

  • coating
  • contact lines
  • interfacial flows (free surface)

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