Marangoni Effect

From Soft-Matter
Jump to: navigation, search

Definition

WineTears.jpg

The Marangoni effect is the flow of fluid caused by a gradient in surface tension [1,2]. The gradient in surface tension can be caused by a gradient in temperature or chemical concentration [1,2]. Fluid flows from a region with low surface tension to a region with high surface tension as seen clearly in the following video: Marangoni Effect Example 1.

The tears of wine phenomenon seen in the photo to the right is explained by the Marangoni effect. You can observe the phenomenon by swirling some wine in a glass and then setting it down. The thin layer of wine coating the glass above the wine's surface will start developing drops or "tears" which run down the glass. As alcohol evaporates from the thin layer of wine coating the glass, the surface tension increases. Wine is driven from the bulk up the sides of the glass towards the area of high surface tension until a drop forms, and gravity pulls it back down [2].

In the case of wine tears, a gradient in chemical concentration causes the surface tension gradient. Ristenpart et. al. explore a surface tension gradient caused by a thermal gradient across the surface of an evaporating drop.

References

[1] Velarde, Manuel, "Drops, Liquid Layers and the Marangoni Effect," Philosophical Transactions: Mathematical, Physical and Engineering Sciences 356 829-844 (1998).

[2] Mei, C., "Lecture 4: Marangoni flows," Fluid Dynamics Lecture Notes (May 5, 2004).