overflatespenning

Overflatespenning, or surface tension, is the cohesive force at the surface of a liquid that makes the surface behave as if covered by a stretched elastic film. It results from molecular interactions at the air–liquid interface and influences wetting, droplet formation, and capillary action.

At the interface, molecules experience unbalanced forces compared with those in the bulk, creating a higher energy state associated with increasing surface area. The magnitude of overflatespenning depends on temperature, impurities, and surface-active substances. Higher temperatures generally reduce surface tension, while surfactants and impurities lower it by accumulating at the surface and disrupting cohesive forces.

Common values include water at 20 °C with about 72.8 millinewtons per meter (mN/m), decreasing with temperature. Mercury has a much higher surface tension, around 0.5 N/m. Surface tension is measured in newtons per meter (N/m) and can be quantified by methods such as the Wilhelmy plate, pendant-drop, or capillary-rise techniques.

Applications include improving wetting in coatings, enabling droplet formation in inkjet printing, stabilizing emulsions and foams, and driving capillary flow in soils and biological systems. Interfacial tension, the analogous property between two immiscible liquids, plays a central role in oil–water separations, emulsification, and detergency.

Overflatespenning is a foundational concept in surface chemistry and fluid mechanics, with measurements critical for designing processes in agriculture, medicine, chemical engineering, and materials science.