ETH Polymer Physics seminar


2002 -02 -06
14 :15 at ML J 21

Evaluation of Pom-pom Models in Single- and Double-Step Strain Flows

David C. Venerus

Department of Chemical Engineering and Center of Excellence in Polymer Science and Engineering, Illinois Institute of Technology, Chicago, Illinois 60616 USA

The Pom-Pom model of McLeish and Larson has been shown to be capable of describing many important phenomena observed in both shear and elongation flows of branched polymer melts. For example, the multi-mode, differential version of the Pom-Pom model with a single set of parameters quantitatively describes constant strain rate simple shear and uniaxial elongation flows. In this study, we consider single- and double-step shear strain flows using a widely characterized low-density polyethylene melt (Lupolen 1810H). Semi-analytic predictions from the Pom-Pom model in single- and double-step strain flows are compared with experimental observations. Single-step strain flow predictions from the integral and differential forms of the pom-pom model and the pompon model of Oettinger are found to display qualitatively different behavior. We also find, contrary to experimental results, that both the integral and differential multi-mode Pom-Pom models show deviations from time-strain factorability. Despite this, the model gives a reasonable prediction for the strain-dependent damping function when averaged over a range of times. In double-step strain flows, predictions of the Pom-Pom model are found to in consistent with experimental results, but no better (or worse) than those from the K-BKZ and Doi-Edwards models.


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