Foams with viscoelastic continuous phases: changing foam coarsening with an emulsion
Foams are gas bubbles in a continuous phase. They are metastable and disappear in time unless the ageing processes are stopped for example by solidifying the continuous phase, to make solid foams. However, we do not always want solid foams, just more stable “liquid foams”. The challenge is to understand, and thus control, the ageing processes.
One way to change foam stability is by changing the mechanical properties of the continuous phase using a viscoelastic fluid, such as emulsion, colloidal gel, polymer etc. Indeed foams from viscoelastic fluids can be much more stable, slowing down the three ageing processes of coarsening, coalescence and drainage 1 . Many common foamed materials have viscoelastic continuous phases, such as whipped cream or foamed cement.
We work with foamed emulsions 2 . We use oil in water emulsions as the continuous phase, because this allows us to control the emulsion mechanical properties through changing oil volume fraction and drop interactions. We focus on the coarsening of pseudo-2D foams to avoid drainage, and to allow us to follow the foam structure in time.
We show that the elasticity of the continuous phase strongly influences the ripening of foamed emulsions, leading to reduced bubble growth rates. Moreover, we show that emulsion viscoelasticity also affects the foam structure, with the appearance of unrelaxed bubble patterns. The results can lead to a more efficient control of the foam structure and stability.