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FAQ - Frequently Asked Questions
Q1- I learned to think about rheological properties in my mind by relaxation times λ and Maxwell model. Is this way to evaluate wrong method?
Q2- Why is used only complex modulus G* or viscosity η* data and lost valuable information included in the elastic G'(ω) and viscous G''(ω) components? Q3- Is there used any internal relaxation time λ, function or spectra in RheoPower? Q4- Does the used model has the entirely phenomenological or real structure of polymers as a background? Q5- Why the different predicted curves cannot superimpose into a mastercurve? Q6- How accurate are computed MWD results by RheoPower? Q1- I learned to think about rheological properties in my mind by relaxation times λ and Maxwell model. Is this way to evaluate wrong method?No, relaxation times are good and descriptive way to get in estimations of material properties and for educational purposes. The true behaviour of polymer is more complicated and always non-linear for any type modifications of Maxwell model and thus not usable for analyses of polymer structures.This topic is discussed shortly on the wirefames for models page and more thoroughly on the published papers. Q2- Why is used only complex modulus G* or viscosity η* data and lost valuable information included in the elastic G'(ω) and viscous G''(ω) components?We have proven that the measured partition of G' and G'' is not accurate although computed dynamic moduli G* is precise. In other words, some amount of viscous response is actually detected as elastic force or on the contrary. Moreover with RheoPower is possible to get modelled G' and G'' to all types of flows impossible to measure as a function of shear rate and elongation rate.Relaxation modulus and spectrum are calculated later on by the formulas shown in published papers and not used elsewhere in the principle. Q3- Is there used any internal relaxation time λ, function or spectra in RheoPower?No, but the polymer structure function P(ω) is fingerprint of polymer structure. P(ω) is composed elastic P'(ω) and viscous P''(ω) functions giving viscoelasticity not only for dynamic measurements, but as a function of shear rate or time for different type of polymer flows.Q6- How accurate are computed MWD results by RheoPower?At first we have to decide to which results and method we will compare. We get very similar results with PS and the outputs of GPC/SEC, which are easy to measure with both methods. On the other hand with polyolefin samples chromatographic methods are insensitive to LCBs and other branches. GPC/SEC results have relatively good intralaboraty repeatability and very poor apparent interlaboratory reproducibility was observed according to IUPAC© report (2010) .Rheological methods and specially RheoPower are sensitive to all kind branching giving true MWDs.
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