During the PhD of Lucie Ducloué (2011-2014) we investigated the rheological properties of suspensions of bubbles in yield stress fluids through experiments on model systems made of monodisperse bubbles dispersed in concentrated emulsions. Thanks to this highly tunable system, the bubble size and the rheological properties of the suspending yield stress fluid were varied over a wide range. We showed that the macroscopic response under shear of the suspensions depends on the gas volume fraction and the bubble stiffness in the suspending fluid. This relative stiffness can be quantified through capillary numbers comparing the capillary pressure to stress scales associated with the rheological properties of the suspending fluid. We demonstrated that those capillary numbers govern the decrease of the elastic and loss moduli, the absence of variation of the yield stress and the increase of the consistency with the gas volume fraction, for the investigated range of capillary numbers. Micro-mechanical estimates are consistent with the experimental data and provide insight on the experimental results.
Related Papers:
– Rheological behaviour of suspensions of bubbles in yield stress fluids, L. Ducloué, O. Pitois, J. Goyon, X. Chateau, G. Ovarlez, Journal of Non-Newtonian Fluid Mechanics (2015) 215, 31-39
– Coupling of elasticity to capillarity in soft aerated materials, L. Ducloué, O. Pitois, J. Goyon, X. Chateau, G. Ovarlez, Soft Matter (2014) 10, 5093-5098