Mechanism
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 be caused by concentration gradient or by a temperature gradient (surface tension is a function of temperature).
As an example, wine may exhibit a visible effect called "tears", as shown in the photograph. The effect is a consequence of the fact that alcohol has a lower surface tension than water. If alcohol is mixed with water inhomogeneously, a region with a lower concentration of alcohol (greater surface tension) will pull on the surrounding fluid more strongly than a region with a higher alcohol concentration (lower surface tension). The result is that the liquid tends to flow away from regions with higher alcohol concentration—along the tension gradient. This can also be easily demonstrated by spreading a thin film of water on a smooth surface and then allowing a drop of alcohol to fall on the center of the film. The liquid will rush out of the region where the drop of alcohol fell.
The Marangoni number, a dimensionless value, can be used to characterize the relative effects of surface tension and viscous forces.
A very detailed mathematical treatment of this from the point of view of the Navier–Stokes equations and the equations of thermodynamics can be found in the first third of Subrahmanyan Chandrasekhar's Hydrodynamic and Hydromagnetic Stability, originally published in 1961 by Oxford, and republished by Dover in 1981.
Read more about this topic: Marangoni Effect
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