ETH Polymer Physics seminar


2004 -09 -01
10 :15 at HCI H 530

Uniaxial elongational flow at large extension rates: A new challenge for model development

Jan van Meerveld

Polymer Physics, Dept. Materials Science, ETH Zurich

Recent experimental data on a monodisperse PS melts at large extension rates indicates a new scaling behaviour. For large extension rates the extensional stress increases with the square of the extension rate. Actually a universal curve is obtained for melts of different chain length. Present models fail to describe this scaling behaviour. Marrucci and Ianniruberto proposed a new model which is based on the interchain pressure effect, which controls the tube diameter in extensional flows. This model correctly predicts the experimental scaling law of Bach et al.. In this talk we first briefly discuss the data of Bach et al as well as some model prediction of typical models available in the literature. Subsequently the model of Marrucci and Ianniruberto is briefly reviewed and the essential mechanisms are discussed. First the mechanism of the interchain pressure effect is explained. Subsequently the introduction of a new time scale for the interchain pressure effect, which plays an important role in the model. It explains the change in the extensional behaviour with molecular weight as well as the difference between polymer melts and polymer solutions. However the introduction of a new time scale appears to be in disagreement with experimental observations during the stress relaxation after a non-linear step shear, cessation after a stationary shear flow or transient elongation flow as well as with the onset of strain hardening in uniaxial flows. Finally, the influence of finite extensibility is absent in the model which may seem an important ingredient for polymer melts as well as the failure of the stress-optical-rule.


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