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Q & A: soap at surfaces

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Most recent answer: 10/29/2009
Q:
How do soaps and detergents affect surface tension?
- Valentin (age 11)
Bremen, Germany
A:
Detergents generally lower the surface tension of water. The surface tension is a measure of how much extra free energy there is due to the surface layer, as compared to having the same amount of stuff without surfaces. Detergents have one end which has low free energy in air and another that has low free energy in water. By coating the surface, they lower its free energy.

There should be a nice sketch of detergent molecules at a surface, but a quick web search hasn't yet found one.

Mike W.

(published on 10/29/2009)

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