Water Surface Tension Reducer
Date: September 2006
Does anything break the surface tension of water
more than soap?
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.
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.
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Update: June 2012