A practical guide to mitigate edge fracture instability in sheared polymer melts
Abstract: The measurement of nonlinear shear response of viscoelastic materials is often hindered by edge fracture instabilities. The phenomenon was first addressed theoretically by Tanner and Keentok and ever since has attracted the interest of experimentalists and theorists alike. Despite progress, accounting for or mitigating edge fracture remains a challenge, in particular when dealing with strongly viscoelastic materials such as entangled polymer melts. Here, we present and compare different experimental attempts t… Show more
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Cited by 3 publications
References 44 publications
Analysis of startup shear flow data of linear polystyrene blends: is shear stress undershoot caused by transient shear banding?
Startup shear stress data of a well-defined set of binary polystyrene blends consisting of monodisperse blend components were reported recently by Parisi et al. (J Non-Newtonian Fluid Mech 315:105028, 2023). They presented convincing evidence that in the fast flow of melts with narrow molar mass distribution, shear stress undershoot is observed after the overshoot and before approaching the steady state. For blends with broad relaxation time spectra, no undershoot was found. We analyze this data set by comparison with predictions of the rotation zero stretch (RZS) model (Wagner et al. Rheol Acta 63:573–584, 2024), which is generalized here to the multi-mode MRZS model for polymer blends. We confirm that the steady-state shear viscosity of the monodisperse blend components as well as of the binary blends agrees with the viscosity predicted by the Doi-Edwards independent alignment model. As long as there is no undershoot, the RZS model (monodisperse melts) and the MRZS model (binary blends) result in a quantitative description of the full startup curve of the shear stress growth $${\sigma }_{12}^{+}(\dot{\gamma },t)$$ σ 12 + ( γ ˙ , t ) including overshoot and steady state, based solely on the linear viscoelastic characterization. The shear stress undershoot observed at higher shear rates in melts with narrow molar mass distribution is not described by the RZS or MRZS model. However, the analysis of the experimental data shows clear evidence that undershoot occurs only if after the overshoot, the decreasing shear stress at a higher shear rate undercuts the shear stress at lower rates, i.e., only if $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }<0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ < 0 . For blends with broad relaxation time spectra, $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }\cong 0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ ≅ 0 and no undershoot is observed. The hypothesis is made that undershoot is due to transient shear banding, which is initiated in shear stress regimes characterized by $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }<0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ < 0 and which disappears at larger strains when the shear stress growth $${\sigma }_{12}^{+}(\dot{\gamma },t)$$ σ 12 + ( γ ˙ , t ) approaches the steady state $${\sigma }_{12}(\dot{\gamma })$$ σ 12 ( γ ˙ ) with $$\partial {\sigma }_{12}(\dot{\gamma })/\partial \dot{\gamma }>0$$ ∂ σ 12 ( γ ˙ ) / ∂ γ ˙ > 0 . Graphical Abstract
Analysis of startup shear flow data of linear polystyrene blends: is shear stress undershoot caused by transient shear banding?
Startup shear stress data of a well-defined set of binary polystyrene blends consisting of monodisperse blend components were reported recently by Parisi et al. (J Non-Newtonian Fluid Mech 315:105028, 2023). They presented convincing evidence that in the fast flow of melts with narrow molar mass distribution, shear stress undershoot is observed after the overshoot and before approaching the steady state. For blends with broad relaxation time spectra, no undershoot was found. We analyze this data set by comparison with predictions of the rotation zero stretch (RZS) model (Wagner et al. Rheol Acta 63:573–584, 2024), which is generalized here to the multi-mode MRZS model for polymer blends. We confirm that the steady-state shear viscosity of the monodisperse blend components as well as of the binary blends agrees with the viscosity predicted by the Doi-Edwards independent alignment model. As long as there is no undershoot, the RZS model (monodisperse melts) and the MRZS model (binary blends) result in a quantitative description of the full startup curve of the shear stress growth $${\sigma }_{12}^{+}(\dot{\gamma },t)$$ σ 12 + ( γ ˙ , t ) including overshoot and steady state, based solely on the linear viscoelastic characterization. The shear stress undershoot observed at higher shear rates in melts with narrow molar mass distribution is not described by the RZS or MRZS model. However, the analysis of the experimental data shows clear evidence that undershoot occurs only if after the overshoot, the decreasing shear stress at a higher shear rate undercuts the shear stress at lower rates, i.e., only if $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }<0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ < 0 . For blends with broad relaxation time spectra, $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }\cong 0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ ≅ 0 and no undershoot is observed. The hypothesis is made that undershoot is due to transient shear banding, which is initiated in shear stress regimes characterized by $$\partial {\sigma }_{12}^{+}(\dot{\gamma },t)/\partial \dot{\gamma }<0$$ ∂ σ 12 + ( γ ˙ , t ) / ∂ γ ˙ < 0 and which disappears at larger strains when the shear stress growth $${\sigma }_{12}^{+}(\dot{\gamma },t)$$ σ 12 + ( γ ˙ , t ) approaches the steady state $${\sigma }_{12}(\dot{\gamma })$$ σ 12 ( γ ˙ ) with $$\partial {\sigma }_{12}(\dot{\gamma })/\partial \dot{\gamma }>0$$ ∂ σ 12 ( γ ˙ ) / ∂ γ ˙ > 0 . Graphical Abstract
Tanner: 90 years of Rheology
No abstract
REVIEW: Nonlinear shear rheometry: Brief history, recent progress, and challenges
High-shear rate rotational rheometry provides access to the fast nonlinear dynamics of soft materials and, particularly, their shear stress (exhibiting shear thinning and/or thickening) as well as the first and second normal stress differences, along with their time-dependent behavior. These material functions are valuable for understanding a material's processing performance and constitutive behavior and, hence, for designing new materials with desired rheology. However, their accurate measurement has been one of the most formidable challenges in rheometry. Here, we provide an overview of the different approaches used, along with their merits and drawbacks, while we discuss practical guidelines for the implementation of measurement protocols. We focus on the development and use of cone-partitioned plate fixtures, which have been shown to provide reliable data over a wide range of Weissenberg numbers, when properly used. Furthermore, this review presents selected applications and results from recent developments, identifies operating measurement windows, discusses new capabilities and open problems, and, finally, it provides perspectives for further developments.
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