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Name: Nathan
Status: student
Grade: 6-8
Location: NC
Country: N/A
Date: September 2006

Question:
Does anything break the surface tension of water more than soap?



Replies:
Fluorochemicals and some silicone compounds reduce the surface tension of water from 72 ergs/cm^2 to less than 20 ergs/cm^2. They are generally the most potent surface tension reducing agents.

Vince Calder


Nathan,

Soap is a general term that describes a mixture of ingredients that are used for cleaning dirt and grim using water as the primary solvent. The active chemicals in the soap are such that half of the molecule is hydrophobic (water fearing) and half of the molecule is hydrophillic (water loving). Mostly these types of molecules are called detergents if they are used for cleaning. Living cells also use this type of molecule, and in this sense it is called a lipid. If your skin did not repel water on the outside and retain it on the inside, think what would happen! Lipids are much more complicated though, so I will stick to detergents.

Dirt molecules are generally greasy (hydrophobic) and tend not to dissolve in water very well. It is the hydrophobic half of the detergent that interacts with the greasy molecules because "like dissolves like". This means that hydrophillic solvents and liquids will dissolve other hydrophillic solids and hydrophobic solvents and liquids will dissolve other hydrophobic substances. This is why oil and vinegar (water) do not mix! Anyway, a bunch of the detergent molecules will surround (solvate) the dirt particle so that it is effectively dissolved in a sphere of detergent. The hydrophillic ends of the detergent are dangling around in the water. This complex is called a "micel" (pronounced: my-cell) and is the essence of how detergents work.

As far as specific chemicals that work "better" than others, it fully depends on what you are trying to trap in the micel--so there is no straightforward answer.

Matt Voss



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