From: SFPhysics@aol.com
Date: Sat Apr 05 2003 - 14:02:38 PST
From: SFPhysics@aol.com Message-ID: <184.18ff99dc.2bc0ac7e@aol.com> Date: Sat, 5 Apr 2003 17:02:38 EST Subject: Warm/Cold water and cleaning
<<
>Subject: Warm/cold water and cleaning
>From: "Geoff Ruth" <gruth@leadershiphigh.org>
>Date: Wed, 26 Mar 2003 20:57:53 -0800
>This feels like a foolish question, but I've never really understood
>why warm water cleans things better with soap. One of my student
>asked me why this was, and I didn't know.
>>
Dear Geoff:
No one seems to have wanted to answer your question so I will make a stab at
it.
It is all about the surface tension of water. Water molecules are cohesive,
that is they like to stick to each other. As temperature rises the thermal
vibration of the molecules lessens the cohesive forces. All the while that
the temperature rises the "wetting factor" increases as the surface tension
lowers. Thus hot water is "wetter" than cold water. When the temperature of
the boiling point of water is reached then molecules have very low cohesion
and leave in the form of a gas. Water is at its wettest when at the boiling
point. In olden times clothing was often washed in a large boiling kettle
with no soap at all.
When a surfactant is used to increase wetting factor it will work better at
higher temperatures because the water is also "wetter." Detergent molecules
and soaps that are used to break up the surface tension of water increase its
"wetting" ability and warmer wetter water makes the effect even more
pronounced.
The second effect of detergent molecules is to link up the bipolar water
molecules with the nonpolar oil or grease molecule. The heat changes the
viscosity of the grease or oils to allow for a greater chemical interaction.
Since chemical reactions work more rapidly at higher temperatures the
detergent reacts with the materials to be removed at a faster rate.
Thus you have two effects happening in warmer water, the surface tension is
lower, and the molecules are more active.
Al Sefl
Whose theories are usually all wet...
And he asks the question:
Would Washer Women With Wetter Water Wash Wonderfully Without Wisk?
Won Wonders?
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