They certainly could.

Another material that shows this behavior is rubber - you can demonstrate it
with a rubber band.

When I was a grad student, we worked through why this is.  I don't remember
all the details, however I believe it hinged on the idea that you model
rubber as a long molecule that folds over on itself many, many times.  You
then show that the entropy decreases as the molecule is stretched (because
it has less ways to fold over on itself), and from this deduce that the CTE
is negative.

I would guess that a polymer which is a long folded molecule, could also
exhibit a negative CTE.

David Nemeth
Senior Process Engineer
Sophia Wireless, Inc.
14225-C Sullyfield Circle
Chantilly, VA
Ph: (703) 961-9573 x206
Fax:(703) 961-9576

-----Original Message-----
From: mems-talk-admin@memsnet.org [mailto:mems-talk-admin@memsnet.org]On
Behalf Of cortese
Sent: Saturday, July 20, 2002 6:25 AM
To: 'Mems-Talk
Subject: [mems-talk] Negative CTE of polymers


Dear All
I'm trying to understand if polymers could show a negative CTE.
I found out a commercial polymer ( a merchapto thiol resin) where they show
a negative CTE (coefficient of thermal expansion) in the range (0-1500C).
Could someone explain that or suggest me some literature about that
phenomena?
Best Regards
Andrea
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