Hot versus Cold Water for Cleaning
Why do white cotton socks seem to
get cleaner in hot water than in cold water?
White socks, eh? Usually white socks used with
tennis shoes get quite dirty.
When you wash them using common soap or detergent
cleaning at machine or by hand means to take off
the dirt from the fabric. Mostly detergents have
ingredients that are more soluble in hot water than in
cold one and that make them to work better.
Also the fabric itself in hot water gets more soft
the thread opens letting the dirt to get loose,
and the fabric gets cleaner.
All that happens with any kind of cloth not only
(Dr. Mabel Rodrigues)
It is not an illusion, Camile. They really do get cleaner.
Heat almost always makes cleaning more aggressive, in any setting.
I can think of three common behaviors that contribute to this:
1) increased reaction rates - (kinetics)
Heat speeds up all reactions, even those as humble as
water wetting it's way along the interface between some slime
and the fiber of your clothing.
2) increased dissolving abilities - (due to entropy)
Even without soap, small amounts of some greases will dissolve
In hot water, the amount that will dissolve can be ten times higher.
3) melting -
Some greases are low-melting waxes, and being melted makes it easier
for the soapy water to penetrate, detach, and surround them.
Even things that are not quite melted at least get softer.
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Update: June 2012