The implementation of a cone-partitioned plate (CPP) is established as a practical way to delay edge fracture effects on the measurement of the nonlinear shear viscosity of polymer melts. A CPP allows us to measure the first and second normal stress differences, N1 and N2, by using at least two different loadings, i.e., two radii of the inner plate (measuring tool) and/or the outer plate (partition). This two-step method works satisfactorily at intermediate shear rates (corresponding to the Rouse–Weissenberg number ). However, it involves significant errors at high shear rates because the shape of the outer edge is involved in the determination of normal stress differences. We present two methods to reliably measure N1 and N2 in entangled polymer melts. The first is based on the use of CPP with a ring collar (CPP-R), which was recently shown to optimally mitigate edge fracture. In this context, we also present the design of a modified partition with the collar embedded in it, CPP-RS, that is easier to align and reduces compliance effects. The data are in excellent agreement with the respective CPP data (with less unambiguous normal stress signal), as well as the reference data from the literature, and are well described by a recent tube-based model. Obtaining stable normal stress signals over long times is essentially a prerequisite for robust N1 and N2 data. Second, we propose a new single-step method based on single loading, by accounting for the onset of edge fracture at the outer partition and its end when it propagates to the inner measuring tool, and the measured signal deviates from the steady state. The very good agreement of the data from different methods, as well as with the tube-model theoretical predictions, suggests that reliable, normal stress difference data of strongly viscoelastic materials can be obtained systematically.
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May 2025
Research Article|
March 10 2025
Normal stress rheometry of polymer melts with partitioned plate fixtures
Benke Li
;
Benke Li
1
Institute of Electronic Structure and Laser, FORTH
, Heraklion 70013, Greece
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Antonios Mavromanolakis
;
Antonios Mavromanolakis
1
Institute of Electronic Structure and Laser, FORTH
, Heraklion 70013, Greece
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Dimitris Vlassopoulos
Dimitris Vlassopoulos
a)
1
Institute of Electronic Structure and Laser, FORTH
, Heraklion 70013, Greece
2
Department of Materials Science and Engineering, University of Crete
, Heraklion 70013, Greece
a)Author to whom correspondence should be addressed; electronic mail: [email protected]
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Benke Li
1
Antonios Mavromanolakis
1
Dimitris Vlassopoulos
1,2,a)
1
Institute of Electronic Structure and Laser, FORTH
, Heraklion 70013, Greece
2
Department of Materials Science and Engineering, University of Crete
, Heraklion 70013, Greece
a)Author to whom correspondence should be addressed; electronic mail: [email protected]
J. Rheol. 69, 253–265 (2025)
Article history
Received:
January 11 2025
Accepted:
February 17 2025
Citation
Benke Li, Antonios Mavromanolakis, Dimitris Vlassopoulos; Normal stress rheometry of polymer melts with partitioned plate fixtures. J. Rheol. 1 May 2025; 69 (3): 253–265. https://doi.org/10.1122/8.0000977
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