Simply put, the steady state shear viscosity at a given shear rate is equal to the dynamic viscosity at the same frequency:
h() = h*(w) when = wThe rule is more-or-less empirical - it works for many common polymers but there is no (strong) theoretical background that it should work for all polymers and it certainly doesn't.
I'm always happy with anyone asking me the question as it is a terrific one and shows that the person is seriously thinking about what is being tested. There are way too many tests that do not match up with reality in the least, and too many people do not question the differences.
It is useful article , thank you
I knew that the Polymer nanocomposites do not obey the cox-merz relation.
My Q is
Does (Cox-Merz) work with Polyethylene terphthalate (PET)? I could not find any study talking about this?
It certainly does work. Here's a link to pages in a book I found showing data. (Look at Figure 12.2 on page 316.)
Thank you John; I got it and it was in agreement with my results.
I am studying the rhological behaviour of PET nanocomposites
Sorry Mr. John;
I forget to ask you Q!
Why PET does not obey Cox-Merz while PP and most of the homo-polymer obey it?
And, I comment under this post.
I see many people do dynamic test, often using TTS, to evaluate the zero-shear viscosity (exactly, the zero-frequency complex viscosity). This process bases on the validity of the Cox-Merz rule but in most of these cases people don't confirm this validity first
Typically a liquid like terminal zone of G'~w^2 and G''~w always gives a plateau of complex viscosity. Whether or not this viscosity value always equals to the zero shear value under steady state flow test is problematic.
Hi but this is only valid on molecular based systems? what about food suspensions?
Try it and see. I wouldn't expect it to be the case as the items you are talking about are of a more complex structure and those are the types of materials that struggle with the rule. But again, try it and see.
I would think not. This rule does not apply to dilute solutions of polysaccharides or anything with strong hydrogen bonding. It works for homoploymers because the underlying model includes only the weak associative forces of each macromolecule when they slide against each other.
I have run across one article that was able to describe this relationship for fluids with a yield stress which more common in food stuffs.
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