Enhanced stability of free viscous films due to surface viscosity

Choudhury, Anjishnu and Paidi, Venkatesh Kumar and Kalpathy, Sreeram K. and Dixit, Harish N. (2020) Enhanced stability of free viscous films due to surface viscosity. Physics of Fluids, 32 (8). 082108. ISSN 1070-6631

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The stability of a thin liquid film bounded by two free surfaces is examined in the presence of insoluble surface-active agents. This study is broadly aimed at understanding enhanced stability of emulsions with the increasing surface concentration of surface-active agents. Surface-active agents not only cause gradients in surface tension but could also render surface viscosity to be significant, which could vary with surface concentration. We employ two phenomenological models for surface viscosity, a linear viscosity model and a nonlinear viscosity model. In the latter, surface viscosity diverges at a critical concentration, which is termed the "jamming"limit. We show that rupture can be significantly delayed with high surface viscosity. An analysis of the "jamming"limit reveals that Γi(nl)>3D/M provides a simple criterion for enhanced stability, where Γi(nl), D, and M are the normalized initial surfactant concentration, disjoining pressure number, and Marangoni number, respectively. Nonlinear simulations suggest that high surface viscosity renders free films remarkably stable in the jamming limit, and their free surfaces behave like immobile interfaces consistent with experimental observations. Furthermore, it is shown that rupture times can be arbitrarily increased by tuning the initial surfactant concentration, offering a fluid dynamical route to stabilization of thin films.

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IITH Creators:
IITH CreatorsORCiD
Dixit, Harish NagarajUNSPECIFIED
Item Type: Article
Uncontrolled Keywords: Critical concentration; Disjoining pressures; Enhanced stability; Nonlinear simulations; Nonlinear viscosity; Phenomenological models; Surface concentration; Surfactant concentrations
Subjects: Physics > Mechanical and aerospace
Divisions: Department of Mechanical & Aerospace Engineering
Depositing User: . LibTrainee 2021
Date Deposited: 02 Aug 2021 05:53
Last Modified: 08 Mar 2022 10:42
URI: http://raiith.iith.ac.in/id/eprint/8629
Publisher URL: http://doi.org/10.1063/5.0016282
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