Yield stress and elasticity influence on surface tension measurements

Abstract

We have performed surface tension measurements on carbopol gels of different concentrations and yield stresses. Our setup, based on the force exerted by a capillary bridge on two parallel plates, allows to measure an effective surface tension of the complex fluid and to investigate the influence of flow history. More precisely the effective surface tension measured after stretching the bridge is always higher than after compressing it. The difference between the two values is due to the existence of a yield stress in the fluid. The experimental observations are successfully reproduced with a simple elasto-plastic model. The shape of successive stretching-compression cycles can be described by taking into account the yield stress and the elasticity of the gel. We show that the surface tension ${\gamma }_{LV}$ of yield stress fluids is the mean of the effective surface tension values only if the elastic modulus is high compared to the yield stress. This work highlights that thermodynamical quantities measurements are challenged by the fluid out-of-equilibrium state implied by jamming, even at small scales where the shape of the bridge is driven by surface energy. Therefore setups allowing deformation in opposite directions are relevant for measurements on yield stress fluids.

arXiv comment12 pages, 16 figures in Soft Matter 2015

References in corpus (6)

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• From transient fluidization processes to Herschel-Bulkley behavior in simple yield stress fluids
• Stress overshoot in a simple yield stress fluid: an extensive study combining rheology and velocimetry
• Capillary Pressure and Contact Line Force on a Soft Solid
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Cited by in corpus (8)

• Power-law creep and residual stresses in a carbopol microgel
• Spreading of viscoplastic droplets
• Acoustic Bubble Dynamics in a Yield-Stress Fluids
• Spreading of droplets under various gravitational accelerations
• Thixotropy in Viscoplastic Drop Impact on Thin Films
• Immersed Cantilever Apparatus for Mechanics and Microscopy
• Yield Stress Fluids Solidifying in Capillary Imbibition
• Capillary and priming pressures control the penetration of yield-stress fluids through non-wetting 2D meshes