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Article Dans Une Revue Journal of Rheology Année : 2023

Instant yield stress measurement from falling drop size: The “syringe test”

Résumé

We analyze different flow regimes of a filament formed by extrusion of a material through a cylindrical die. We deduce that the elongational yield stress of a simple yield stress fluid (i.e., with negligible thixotropy effects) can be determined from the mass of the droplet after filament breakage and an estimation of the critical radius at pinch-off at the solid-liquid regime transition. We demonstrate that such a simple characterization is relevant in a relatively wide range of extrusion velocities, i.e., this velocity slightly affects the drop mass in this range. For the simple yield stress fluids used, Carbopol gel, clay-water paste at different concentrations, and emulsion, covering a large range of yield stress values (50–1000 Pa), the elongational yield stress appears to be equal to the simple shear yield stress times a factor equal to about 1.53. As a consequence, this simple test may be used to obtain, almost instantaneously and without sophisticated apparatus (a syringe and a balance are sufficient), a good estimate of the shear yield stress of simple yield stress fluids. In that case, the main source of uncertainty (up to about 20%) is the value of the critical radius at the solid-liquid transition. Finally, we review the operating conditions (material properties and extrusion characteristics) for which we can expect this approach to be valid.
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Dates et versions

hal-04248509 , version 1 (17-07-2024)

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Anatole Geffrault, Hela Bessaies-Bey, Nicolas Roussel, P. Coussot. Instant yield stress measurement from falling drop size: The “syringe test”. Journal of Rheology, 2023, 67 (2), pp.305-314. ⟨10.1122/8.0000557⟩. ⟨hal-04248509⟩
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