Marangoni effect

Summary

The Marangoni effect is the flow of a liquid along an interface driven by differences of surface tension along that interface. Surface tension can vary because of temperature or because of the concentration of a dissolved substance or surfactant. Regions of high surface tension pull harder on the surface than regions of low surface tension. So the surface and the liquid below it move towards high surface tension. The effect drives the "tears of wine", the spreading of soap on water, and convection cells in thin heated liquid layers. It also matters in welding and crystal growth.