PSS (polystyrene sulfonate) viscosity....
Is it because of the charge of PSS (PSS is an ionomer)? How to explain the viscosity difference in terms of polymer structure? Thanks.
First of all the density,the molecular weight, the intermolecular distance, the correlation length and size of of the chemical structure, finally the Van der interaction
Probably because one of polyelectrolte (NaPSS) is a strong polyelectrolyte and poly-lactitic is a weak polyelectrolyte...
When discussing polymer viscosity one must remember that viscosity is related to the reference temperature of the material (difference in measurement temperature above that of the glass transistion temperature). Only at the same reference temperature can fair comparisons between polymer viscosities be made. This is assuming that you are talking about the polymers in the melt state (no plasticizer or diliuent, not a polymer gel).
I recommend you read this book "Polyelectrolytes: Thermodynamics and Rheology" Series: Engineering Materials: P. M., Visakh, Bayraktar, Oguz, Pico, Guillermo Alfredo (Eds.) 2014
It's relatively easy to predict changes in viscosity with concentration or molecular weight, so if you just want solutions of each polymer that are similar in viscosity, then this is easily achievable. (Cowie and Arrighi's book gives a good accessible introduction to the underlying science.) However, if you are after reasons why, this is much more difficult. When the chemistry of the repeat unit is changed, you are changing the polymer - polymer interactions, the polymer - solvent interactions, the dissociation constant of any ions present, and the intramolecular interactions within the polymer chain, which influence the Tg (see Schaeffer, above).
There is not enough data to provide a meaningful answer. Are you talking about solution or melt viscosity? Probably it is solution. If so, what concentrations in what solvent were used? Were the polymers in acid or salt form? Did the solvent have added salts? These questions must be answered before any reasonable response can be made. A polymer in a poor solvent could have a low intrinsic viscosity, while in a good solvent the same polymer could have a high intrinsic viscosity.
I agree with some comments posted above. When we compare viscosity of two different polymers, we first need to know if it refers to the viscosity of polymer melts or solutions. If it is regarding solutions, we then need to specify the solvent, temperature, and polymer concentration. Please note that PSS is a water-soluble polyelectrolyte while poly(lactic acid) (PLA) is a water-insoluble polyester (plastic). Hence the knowledge about the type of solvent and solution conditions is essential for answering this question.
First of all the density,the molecular weight, the intermolecular distance, the correlation length and size of of the chemical structure, finally the Van der interaction
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