This behavior was exhibited by thermoplastic polymer functionalized on molten state
In case of polymers - the shear viscosity depends on chain flexibility /chain structure.
Regards, Leonid
Dear Dr. Edwin,
though the question is still ambigous for me, I think this is a behavior may be noticed for thermoplastics-elastomers. I think during functionalization some low level of curing or crosslinking has occured. Please if you can add more clarifications. Regards
The chain flexibility (the ability of polymer chain align with the shear direction) - is important - for lower shear viscosity; whereas in case of complex viscosity important is concentration.
Regards, Leonid
The question is not correct or need more clarification. Complex viscosity against frequency/shear rate (is also in shear mode) usually obtain at wide range of frequency by not at high shear rates. To be helpful, the complex viscosity-shear rate curve and shear viscosity - shear rate curve should be in front. Don't forget to consider and check the validity of Cox-Merz rule.
The complex viscosity measurements carry out in linear viscoelastic range of deformation at a predetermined strain amplitude. In steady shear measurement the required shear stress obtain at any applied shear rate . It can be expected that at very low shear rates the viscosity-shear rate (flow curve results) should have nearly the same trend as dynamic oscillation measurement.
The complex viscosity measurements carry out in linear viscoelastic range of deformation at a predetermined strain amplitude. In steady shear measurement the required shear stress obtain at any applied shear rate . It can be expected that at very low shear rates the viscosity-shear rate (flow curve results) should have nearly the same trend as dynamic oscillation measurement.
Simply on shear viscosity you disturb the structure i.e. measured value depends on the changed solution properties. In contrast for the complex viscosity we define shear stress and frequency values (in LVER region) in order to not disturb, or limit, the structural changes. Therefore we stay in the linear viscoelastic region (LVER) during the whole experiment (at least what you are suppose to do).
If the measurement is done within the low frequency/low shear rate range and at low enough strain amplitude to remain in the viscoelastic region, then for each sample whether it is A or B, the complex viscosity versus frequency curve and the shear viscosity versus shear rate curve should match in accordance with the Cox-Mertz rule. However, in this particular case, since the complex viscosity and the shear viscosity curves for samples A and B reverse trends, it is obvious that the frequency range and the shear rate range are outside the validity of the Cox-Mertz rule and/or applied strain amplitude is not low enough to keep the measurement in the linear viscoelastic region. The probable explanation for the reversal trend lies in the possibility that the sample A which has a higher complex viscosity is far more sensitive to shear resulting in far greater breakdown of the structure than sample B. A strain amplitude sweep measurement on the two samples should prove that. A good way to confirm trends would be to compare master curves for the two samples rather than making comparisons at a specific temperature and limited frequency or shear rate range. Unification of data for creating such master curves is discussed in the following books and may be helpful.
A. V. Shenoy and D. R. Saini, Thermoplastic Melt Rheology and Processing, Marcel Dekker Inc., New York (1996).
Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).
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