A surfactant is an interfacially active substance that changes surface tension. A concentration gradient therefore generates tangential Marangoni stress.
Outward interfacial flow from a thinning region dilutes surfactant there and raises its surface tension. The resulting Marangoni stress pulls fluid back toward the thinning region, opposes further stretching, and slows rupture.
An insoluble surfactant remains on an interface. Without surface diffusion, its material concentration changes only through the local surface-area dilation rate.
The Marangoni effect is interfacial flow driven by a surface-tension gradient. Tangential stress balances the surface gradient .
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Surfactant, short for surface-active agent, is a substance that reduces surface tension in liquids. Surfactants are typically amphiphilic molecules, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. This unique structure allows them to accumulate at interfaces, such as between air and water or oil and water, altering the properties of the surface.