Rheological behavior of entangled polymer melts and solutions in fast extensional flow
Invited
Abstract
Extensional rheology of polymer liquids is highly sensitive to molecular architecture. Accurate and reliable stress-strain measurements of extensional flow play a crucial role in understanding the nonlinear rheological properties of polymers. However, extensional flow is difficult to measure reliably.
In the first part of this presentation, we compare the stress-strain measurements of entangled polymer melts and solutions between two types of state-of-the-art extensional rheometers, namely the Sentmanat extensional rheometer (SER) and the filament stretching rheometer (FSR). While necking instabilities, which prevent steady flow, are observed in SER at some specific range of normalized stretch rate (Weissenberg number), kinematically steady extensional flow can be achieved in FSR with the help of an online control scheme [1]. At higher Weissenberg numbers, elastic fracture happens in both SER and FSR [1]. The significance of the observed necking, steady extensional flow, and elastic fracture will be discussed in the presentation.
In the second part, we show the results of extensional rheology measured in FSR for entangled polymer liquids with different molecular architectures, including linear, star, comb, and ring polymers. Some results are also compared with the ones measured in SER. Interpretation of the rheological results will be presented and compared with the results from ex-situ small angle neutron scattering (SANS). Furthermore, stress relaxation measurements following steady extensional flow for a linear polymer melt will be presented, together with the corresponding results of ex-situ SANS. We show that the chain stretch idea in the tube model can be critically tested through analyzing the SANS data at different time in stress relaxation process.
[1] Q. Huang and O. Hassager, Soft Matter 2017, 13, 3470-3474.
In the first part of this presentation, we compare the stress-strain measurements of entangled polymer melts and solutions between two types of state-of-the-art extensional rheometers, namely the Sentmanat extensional rheometer (SER) and the filament stretching rheometer (FSR). While necking instabilities, which prevent steady flow, are observed in SER at some specific range of normalized stretch rate (Weissenberg number), kinematically steady extensional flow can be achieved in FSR with the help of an online control scheme [1]. At higher Weissenberg numbers, elastic fracture happens in both SER and FSR [1]. The significance of the observed necking, steady extensional flow, and elastic fracture will be discussed in the presentation.
In the second part, we show the results of extensional rheology measured in FSR for entangled polymer liquids with different molecular architectures, including linear, star, comb, and ring polymers. Some results are also compared with the ones measured in SER. Interpretation of the rheological results will be presented and compared with the results from ex-situ small angle neutron scattering (SANS). Furthermore, stress relaxation measurements following steady extensional flow for a linear polymer melt will be presented, together with the corresponding results of ex-situ SANS. We show that the chain stretch idea in the tube model can be critically tested through analyzing the SANS data at different time in stress relaxation process.
[1] Q. Huang and O. Hassager, Soft Matter 2017, 13, 3470-3474.
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Presenters
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Qian Huang
Technical University of Denmark, Department of Chemical and Biochemical Engineering, Technical University of Denmark
Authors
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Qian Huang
Technical University of Denmark, Department of Chemical and Biochemical Engineering, Technical University of Denmark