Marangoni effect

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The Marangoni effect (sometimes also called the Gibbs-Marangoni effect) is the mass transfer on, or in, a liquid layer due to surface tension differences.

Since a liquid with a high surface tension pulls more strongly on the surrounding liquid than one with a low surface tension, the presence of a gradient in surface tension will naturally cause the liquid to flow away from regions of low surface tension. The surface tension gradient can in turn be caused by concentration gradient - ethanol concentration , in the case of "tears of wine" - or by a temperature gradient. (Surface tension is a function of temperature.)

Under earth conditions the effect of gravity inducing density driven convection in a system with a temperature gradient along a fluid/fluid interface is usually much stronger than the marangoni effect. Many experiments (ESA MASER 1-3) have been conducted under microgravity conditions aboard sounding rockets to observe the marangoni effect without the influence of gravity.

This phenomenon was first identified in the so called "tears of wine" by physicist James Thomson (Lord Kelvin's brother) in 1855. The general effect is named after Italian physicist Carlo Marangoni, who studied it for his doctoral dissertation at the University of Pavia and published his results in 1865. The most complete early treatment of the subject is due to Willard Gibbs.

Another instance of the Marangoni effect appears in the behavior of convection cells, the so-called Bénard cells.