lowsurfacetension

Low surface tension refers to liquids whose surface tension is substantially lower than that of water at a given temperature. Surface tension is the cohesive force at a liquid–air interface, which tends to minimize surface area. Water has a relatively high surface tension around 72 mN/m at 20°C, so liquids with much lower values are described as having low surface tension. Common examples include many organic solvents such as hexane (about 18–20 mN/m) and ethanol (about 22 mN/m), as well as various oils and fluorinated liquids.

Low surface tension can be intrinsic to the liquid or achieved by adding surface-active agents called surfactants. Surfactants reduce interfacial tension by concentrating at interfaces, improving wetting, spreading, and emulsification. Temperature also decreases surface tension; for most liquids, surface tension falls as temperature rises, which can influence performance in processing and applications.

Measurement of surface tension is commonly performed with methods such as the Du Noüy ring or the Wilhelmy plate, as well as pendant-drop techniques. Values are sensitive to temperature, purity, and contamination; even trace amounts of surface-active impurities can markedly alter measurements and behavior at interfaces.

Applications and implications include coatings, inkjet printing, spray technologies, and cleaning processes, where low surface tension liquids promote spreading and thinning. In microfluidics and biomedical contexts, they enable easier flow through narrow channels. Safety and environmental considerations are important for low surface tension liquids, as many are volatile or flammable, and surfactants vary in biodegradability and ecological impact.