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pps proceeding
Symposium: Rheology & Advanced Characterization
Poster Presentation
 
 

On estimating the zero-shear-rate viscosity: Tests with PIB and PDMS

Shaw Montgomery (1)*

(1) University of Connecticut - Connecticut - USA

The zero-shear-rate viscosity is of fundamental importance for examining the influence of structural or thermodynamic variables on rheological behavior. Unfortunately, such cannot be measured directly because it is a ratio of two variables (stress and strain rate) where both approach zero. While we can anticipate that stress will vary linearly with strain rate at a low-enough strain rate, this is often very difficult to observe because of the issues of reaching steady state and polymer degradation during prolonged experiments. Thus, extrapolation of high-rate data using common empirical models is normally practiced or even required. At the International Congress on Rheology in 2012, it was reported that there were certain pairs of models that would reliably bracket the true value of the zero-shear-rate viscosity using high-rate data, but the effectiveness of this approach was tested using only one polymer, a poly(dimethyl siloxane) (PDMS). This work has been extended using polyisobutylene (PIB), a polymer with much more complex viscoelastic response. While finding two models to bracket the value is relatively straightforward, the result may not be practical because the bracketing values may be quite far apart. Thus, also considered in this work was the question of improving the prediction accuracy by using a method analogous to Romberg integration along with a distribution of predicted values.