Beware of CaBER: Filament thinning rheometry does not always give `the' relaxation time of polymer solutions
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| Format: | Preprint |
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2023
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| _version_ | 1866916335644049408 |
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| author | Gaillard, Antoine Gutierrez, Miguel Angel Herrada Deblais, Antoine Eggers, Jens Bonn, Daniel |
| author_facet | Gaillard, Antoine Gutierrez, Miguel Angel Herrada Deblais, Antoine Eggers, Jens Bonn, Daniel |
| contents | The viscoelastic relaxation time of a polymer solution is often measured using Capillary Breakup Extensional Rheometry (CaBER) where a droplet is placed between two plates which are pulled apart to form a thinning filament. For a slow plate retraction protocol, required to avoid inertio-capillary oscillations for low-viscosity liquids, we show experimentally that the CaBER relaxation time $τ_e$ inferred from the exponential thinning regime is in fact an apparent relaxation time that may increase significantly when increasing the plate diameter and the droplet volume. Similarly, we observe that $τ_e$ increases with the plate diameter for the classical step-strain plate separation protocol of a commercial (Haake) CaBER device and increases with the nozzle diameter for a Dripping-onto-Substrate (DoS) method. This dependence on the flow history before the formation of the viscoelastic filament is in contradiction with polymer models such as Oldroyd-B that predict a filament thinning rate $1/3τ$ ($τ$ being the model's relaxation time) which is a material property independent of geometrical factors. We show that this is not due to artefacts such as solvent evaporation or polymer degradation and that it can only be rationalised by finite extensibility effects (FENE-P model) for a dilute polymer solution in a viscous solvent, but not for semi-dilute solutions in a low-viscosity solvent. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2309_08440 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Beware of CaBER: Filament thinning rheometry does not always give `the' relaxation time of polymer solutions Gaillard, Antoine Gutierrez, Miguel Angel Herrada Deblais, Antoine Eggers, Jens Bonn, Daniel Soft Condensed Matter Fluid Dynamics The viscoelastic relaxation time of a polymer solution is often measured using Capillary Breakup Extensional Rheometry (CaBER) where a droplet is placed between two plates which are pulled apart to form a thinning filament. For a slow plate retraction protocol, required to avoid inertio-capillary oscillations for low-viscosity liquids, we show experimentally that the CaBER relaxation time $τ_e$ inferred from the exponential thinning regime is in fact an apparent relaxation time that may increase significantly when increasing the plate diameter and the droplet volume. Similarly, we observe that $τ_e$ increases with the plate diameter for the classical step-strain plate separation protocol of a commercial (Haake) CaBER device and increases with the nozzle diameter for a Dripping-onto-Substrate (DoS) method. This dependence on the flow history before the formation of the viscoelastic filament is in contradiction with polymer models such as Oldroyd-B that predict a filament thinning rate $1/3τ$ ($τ$ being the model's relaxation time) which is a material property independent of geometrical factors. We show that this is not due to artefacts such as solvent evaporation or polymer degradation and that it can only be rationalised by finite extensibility effects (FENE-P model) for a dilute polymer solution in a viscous solvent, but not for semi-dilute solutions in a low-viscosity solvent. |
| title | Beware of CaBER: Filament thinning rheometry does not always give `the' relaxation time of polymer solutions |
| topic | Soft Condensed Matter Fluid Dynamics |
| url | https://arxiv.org/abs/2309.08440 |