450080 Dynamic Wetting Failure in Surfactant Solutions

Wednesday, November 16, 2016: 9:15 AM
Powell I (Parc 55 San Francisco)
Chen-Yu Liu1, Marcio S. Carvalho2 and Satish Kumar1, (1)Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, (2)Mechanical Engineering, Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Brazil

The influence of insoluble surfactants on dynamic wetting failure during displacement of Newtonian fluids in a rectangular channel is studied in this work. A hydrodynamic model for steady Stokes flows of dilute surfactant solutions is developed and evaluated using three approaches: (i) a one-dimensional (1D) lubrication-type approach, (ii) a novel hybrid of a 1D description of the receding phase and a 2D description of the advancing phase, and (iii) an asymptotic theory of Cox (J. Fluid Mech. 168 (1986) 195). Steady-state solution families in the form of macroscopic contact angles as a function of the capillary number are determined and limit points are identified. When air is the receding fluid, Marangoni stresses are found to increase the receding-phase pressure gradients near the contact line by thinning the air film without significantly changing the capillary-pressure gradients there. As a consequence, the limit points shift to lower capillary numbers and the onset of wetting failure is promoted. The model predictions are then used to interpret decades-old experimental observations concerning the influence of surfactants on air entrainment (Burley & Kennedy, Chem. Eng. Sci. 31 (1976) 901). In addition to being a computationally efficient alternative for the rectangular geometries considered here, the hybrid modelling approach developed in this paper could also be applied to more complicated geometries where a thin air layer is present near a contact line.

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