As we all know that after a sudden step strain to the polymeric thick film between parallel plates will result in a stress relaxation with, say, terminal relaxation time equals to T.
So my question is how does the bulk morphology changes between the t=0 and t=T? Is there any sudden forced alignment between the chains? Or is it just the increased stress at the entanglement points?
Assume temperature to be above Tg.
The morphological analysis of stress relaxation is so hard, because the polymeric materials are not real solid. Be careful, the polymers are vico-elastic,so, the prediction of chain condition after relaxation is so hard. In addition, increasing of stress at the entanglement point means residual stress that is meaningless in the case of stress relaxation phenomenon.
Dear Ayob,
Sorry to say. But that doesn't answer my question. Stress at entanglement points or little orientation in the chain, these are the two random possibilities.
Thanks
Stress relaxation is not described in terms of deformation of particular microstructural elements, but more in terms of reconfiguration. For example, the reptation model (for linear polymers) relates stress relaxation to diffusion through snake-like motion . Between t=0 and t=T the "chain" diffuses from the deformed "tube" into a new configuration. So the terminal time is equal to the tube renewal time, or the reptation time.
Interestingly, ring polymers cannot be described by this model but show similar characteristics. Take a look at this paper.
http://www.che.psu.edu/faculty/milner/group/research/full_research/download/rings.pdf
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