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Materials to Limit Melting
Name: John
Status: educator
Grade: 6-8
Location: VA
Country: USA
Date: Spring 2009
Question:
What material could be used to keep soft material such as
lipstick or Chapstick from melting in the sun or a hot car? Is there
something that would actually keep an object at a cooler temperature when
the outside temp is above 100 degrees F?
Replies:
John,
I think the Chapstick is supposed to melt -- that is how it gets spread
onto your lips. I am going to run through several options (heat
absorption, heat transfer, melting point change, and insulation) to
give you an idea of possibilities, although none seem very practical
for Chapstick.
As for a material that simply absorbs heat, there are some basic laws
of science that we butt up against here. The law of conservation of
energy tells us that we cannot just make the heat disappear. To absorb
heat, you might add a chemically reactive system that absorbs heat
(ignoring safety considerations), but eventually the extra heat coming
from the outside has to go somewhere, and the chemicals absorbing the
heat will get depleted. If you add something (or surround it / put it
inside a container) with a slightly lower melting point than the wax,
that material will melt first and the melting process will absorb
energy, and therefore delay the Chapstick from melting. But once the
second material melts, it has done all it can do, and the Chapstick
will melt next.
Another option is to pump the heat out (move it away). This requires
energy input, and there are many types of coolers you could use (ice
packs, which store energy previously used to freeze the ice, or
refrigerators which use electricity as they run, etc.) If the
surrounding air is hot, then you need some kind of energy source to
keep some area cooler than its surroundings.
You could also simply prevent (slow down) the hot surroundings from
heating the Chapstick. This is known as insulation. There are a
million insulated containers - Thermos' and insulated boxes
(coolers), etc. You could design an insulated Chapstick container, but
probably not a practical one. And all insulation does is buy time --
eventually the cooler, and the Chapstick in a cooler, will reach
ambient (hot) temperature and melt.
The bottom line is, you cannot block the heat indefinitely, you cannot
absorb the heat indefinitely, and you need energy to pump it away. If
you cannot block, absorb or pump the heat away, eventually the
Chapstick temperature will rise, and it will melt. So the next
question is if you can change the Chapstick itself.
There are plenty of materials that could be added to the Chapstick to
keep it from melting, but the problem is that they would keep it from
melting, and therefore make it a lot harder to apply to your lips. You
could use a higher molecular weight wax (which has a higher melting
point), and you could add any number of ceramic or polymer additives
(liquids, particles, or fibers) to keep it more solid. Making a harder
Chapstick is easy, but then it does not work well on your lips. You can
also modify its viscosity at different temperatures -- for example, by
making it "thicker" at higher temperatures. You could even design it
to be "shear thinning" which means it only flows when you apply a
stress (like rubbing it on your lips), but does not flow when just
sitting in a container. But this also would not be good for Chapstick
because as soon as you try to advance the stick, it would flow.
Hope this helps,
Burr Zimmerman
You cannot fight the laws of Nature!! There are commercially available
auto-refrigerators. I do not know of any other way to keep the temperature
cool. Except maybe be "not so cool".
Vince Calder
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Update: June 2012
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