Determination of the shear and extensional rheology of bubbly liquids with a shear-thinning continuous phase

The effect of bubble volume fraction, ϕ, and bubble size on the rheology of rheology of κ/ι-hybrid carrageenan gum solutions and bubbly liquids with ϕ ≤ 0.25 was studied in steady shear using a parallel plate configuration and in extension using a filament stretching device. Three different bubble size distributions were prepared using (1) planetary mixing (mean bubble size 90–130 μm), (2) mixing followed by pumping through a symmetric syringe (25–38 μm), and (3) as (2) but using an asymmetric syringe (12–20 μm). Gum concentrations of 10 and 20 g/L, lying in the semi-dilute regime, were studied. The unaerated gum solutions are viscoelastic and could be modelled very well as a single-mode Giesekus fluid. The bubbly liquid behaviour in both shear and extension could also be modelled as a single-mode Giesekus fluid. The Giesekus parameters for the bubbly liquids were related to those of the unaerated solutions by monatonic increasing dependencies on ϕ. The low shear rate apparent viscosity followed the trend predicted by the Choi and Schowalter (Phys Fluids 18: 420, 1975) model for emulsions, while the mobility parameter and relaxation time were linearly dependent on ϕ. In these tests bubble size only affected filament extension noticeably, influencing the mobility parameter. Further work is required to explain the observations in terms of micromechanical models.