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Ian Harper

How Detergents and Surfactant Surface Tension Work

2 min read

How does detergent work? How does it clean your clothes? In understanding how detergents work, you need to understand surfactant surface tension and how it affects the way your detergent works.

Surfactants are one of the key ingredients of any detergent – which is differentiated from soap precisely because of this fact. A basic definition of a surfactant is a substance that significantly reduces the surface tension of a liquid. In the context of using detergents, of course the liquid will be the washing water. Water by itself, because of the way it is bound on the molecular / atomic level, is not enough to wash clothes and remove stains. The binding gives it surface tension, that does not allow it to interact with stains, especially oily ones – the principle behind the saying, “Water and oil do not mix.”

Surfactant surface tension appears as a thin film on top of the water, which is the one responsible for lowering the surface tension of the water. Lowered surface tension makes the water, become “wetter” in a sense, as the liquid spreads out and becomes looser, allowing it to interact with the stain. Surfactants also enable the oils and other stains dissolve in the water through scrubbing or just soaking, and then let it get washed away along with everything in the rinsing process. This effect is made possible through a process called adsorption, which is where this film appears – you’ll notice it in water that’s mixed with detergent.

There are many types of surfactants, anionic, cationic, non-ionic, and amphoteric or zwitterionic surfactants. Each has a particular characteristic, but all have the surfactant surface tension effect. The amount or combination of the two in a detergent depends on the manufacturer and the function of the detergent. Surfactants are also used in different household cleaning aids like dishwashing liquid.