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Liquid surfaces are pulled by the intermolecular forces, which are unbalanced on the boundary, producing surface tension. When liquid layers with different surface tension get in contact, these forces cause a flow, also known as Marangoni effect,1 which is also the origin of the beautiful patterns found in the ancient japanese art of Suminagashi (”floating ink”). In this image, a film of oleic acid surfactant (with surface tension 32.5 mN/m) quickly spreads spontaneously about 2.5 mm over a layer of glycerol (with surface tension 63.4 mN/m). Both Marangoni and capillary stresses cause variations in the film thickness, leading to dendritic flow patterns. The contour lines are interference fringes.
Click image to zoom2
- C. Marangoni, “Über die Ausbreitung der Tropfen einer Flüssigkeit auf der Oberfläche einer anderen”, Ann. Phys. Leipzig, 143:337-354 (1871). [↩]
- © B. J. Fischer, A. A. Darhuber, S. M. Troian, Department of Chemical Engineering, Princeton University [↩]
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