The Marangoni effect refers to the movement of fluid along an interface caused by a gradient in surface tension. When surface tension varies across a liquid’s surface—due to changes in temperature or concentration of solutes—the fluid flows from areas of low surface tension to high surface tension in an attempt to equalize the forces.
This effect leads to mass transfer along the surface or interface, and it plays a vital role in many natural and industrial processes.
Key Causes of Surface Tension Gradients:
- Thermal Marangoni effect: caused by temperature differences (surface tension decreases with increasing temperature).
- Solutal Marangoni effect: caused by differences in concentration of substances like alcohol or surfactants.
Examples:
- Tears of wine: Drops that form on the sides of a wine glass are due to ethanol evaporation causing surface tension gradients.
- Soldering and welding: The flow of molten metal is influenced by the Marangoni effect.
- Microfluidics and inkjet printing: Controlled flows are often driven by Marangoni forces.
The Marangoni effect is essential in understanding fluid stability, evaporation patterns, film formation, and transport processes at fluid interfaces.