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Published December 10, 2005 | public
Journal Article Open

Spreading characteristics of an insoluble surfactant film on a thin liquid layer: comparison between theory and experiment


We describe measurements of the surface slope and reconstruction of the interface shape during the spreading of an oleic acid film on the surface of a thin aqueous glycerol mixture. This experimental system closely mimics the behaviour of an insoluble surfactant film driven to spread on a thin viscous layer under the action of a tangential (Marangoni) surface stress. Refracted image Moiré topography is used to monitor the evolution of the surface slope over macroscopic distances, from which the time variant interface shape and advancing speed of the surfactant film are inferred. The interfacial profile exhibits a strong surface depression ahead of the surfactant source capped by an elevated rim at the surfactant leading edge. The surface slope and shape as well as the propagation characteristics of the advancing rim can be compared directly with theoretical predictions. The agreement is quite strong when the model allows for a small level of pre-existing surface contamination of the initial liquid layer. Comparison between theoretical and experimental profiles reveals the importance of the initial shear stress in determining the evolution in the film thickness and surfactant distribution. This initial stress appears to thin the underlying liquid support so drastically that the surfactant droplet behaves as a finite and not an infinite source, even though there is always an excess of surfactant present at the origin.

Additional Information

© 2005 Cambridge University Press. Reprinted with permission. (Received 14 December 2004 and in revised form 15 May 2005). Published online 18 November 2005 This work was supported by the National Science Foundation (Chemical and Transport Systems), the NASA Microgravity Fluid Physics Program and the Princeton Research Institute for the Science and Technology of Materials. S.M.T. also kindly acknowledges the Moore Distinguished Scholar Program at the California Institute of Technology.


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