Pinch-off of a surfactant-covered jet

Surfactants at fluid interfaces not only lower and cause gradients in surface tension but can induce additional surface rheological effects in response to dilatational and shear deformations. Surface tension and surface viscosities are both functions of surfactant concentration. Measurement of surfa...

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Bibliographic Details
Published in:Journal of fluid mechanics 2021-02, Vol.908, Article A38
Main Authors: Wee, Hansol, Wagoner, Brayden W., Garg, Vishrut, Kamat, Pritish M., Basaran, Osman A.
Format: Article
Language:English
Subjects:
Aquatic reptiles
Asymptotic properties
Deformation effects
Enhanced oil recovery
Interfaces
JFM Papers
Measurement
Measurement methods
Newtonian liquids
Numerical analysis
Rheological properties
Rheology
Similarity solutions
Stresses
Surface tension
Surfactants
Thinning
Viscosity
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Summary:Surfactants at fluid interfaces not only lower and cause gradients in surface tension but can induce additional surface rheological effects in response to dilatational and shear deformations. Surface tension and surface viscosities are both functions of surfactant concentration. Measurement of surface tension and determination of its effects on interfacial flows are now well established. Measurement of surface viscosities, however, is notoriously difficult. Consequently, quantitative characterization of their effects in interfacial flows has proven challenging. One reason behind this difficulty is that, with most existing methods of measurement, it is often impossible to isolate the effects of surface viscous stresses from those due to Marangoni stresses. Here, a combined asymptotic and numerical analysis is presented of the pinch-off of a surfactant-covered Newtonian liquid jet. Similarity solutions obtained from slender-jet theory and numerical solutions are presented for jets with and without surface rheological effects. Near pinch-off, it is demonstrated that Marangoni stresses become negligible compared to other forces. The rate of jet thinning is shown to be significantly lowered by surface viscous effects. From analysis of the dynamics near the pinch-off singularity, a simple analytical formula is derived for inferring surface viscosities. Three-dimensional, axisymmetric simulations confirm the validity of the asymptotic analyses but also demonstrate that a thinning jet traverses a number of intermediate regimes before eventually entering the final asymptotic regime.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2020.801