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hyh
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 Posted: Tue Apr 08, 2008 2:28 am Post subject: What is the meaning of 'relaxation time' in polymer? |
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Hello! everyone
Would you please explain the meaning of relaxtion time in polymer?
Thank you so much |
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Rolf Wissmann
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| Posted: Tue Apr 08, 2008 1:53 pm Post subject: Re: What is the meaning of 'relaxation time' in polymer? |
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The idea of a "relaxation" method is to disturb an existing equilibrium and
watch it decay back to equilibrium. "Relaxation time" is a time constant for
a system to return to equilibrium in response to a sudden disturbance, like
a pressure jump or a temperature jump or .... One can follow the progress of
the reaction as it returns to equilibrium electronically by measuring the
change in some property like electrical conductivity or spectroscopic
absorption, or ...
hyh wrote:
[quote]Hello! everyone
Would you please explain the meaning of relaxtion time in polymer?
Thank you so much[/quote] |
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ljeffler
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| Posted: Wed May 21, 2008 6:52 am Post subject: Re: What is the meaning of 'relaxation time' in polymer? |
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To build on rolf>s statement, in polymers relaxation time typically refers to the time it takes the polymer chains to return to equilibrium after being distrubed in some manner. A classic relaxation time experiment is a stress relaxatioon experiment. One takes a molten polymer in a cone & plate rheometer and apply at fixed strain and measure the decay of the corresponding stress over time. Typically it responds in an exponential manner (more or less). So that
s(t) = so*exp(t/T), where s(t) is the stress as a function of time, so is the initial stress, and T is the relaxation time
Hope this helps
Larry Effler
"hyh" <hwang0505@gmail.com> wrote in message news:16067a87-d1b9-423c-acfb-75a339687d30@u10g2000prn.googlegroups.com...
[quote]Hello! everyone
Would you please explain the meaning of relaxtion time in polymer?
Thank you so much[/quote] |
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