Rheology of steady-state draining foams

We developed the foam drainage rheology technique in order to perform rheological measurements of aqueous foams at a set liquid fraction epsilon and fixed bubble radius R without the usual difficulties associated with fluid drainage and bubble coarsening. The shear stress exhibits a power-law dependence on strain-rate, tau approximately gamma[over]n where n approximately 0.2. The stress exhibits an inverse dependence on liquid content, tau approximately (1+h'epsilon)(-1), where h'=theta(10) exhibits a diminishing logarithmic trend with gamma[over]. We propose a model based upon film shearing as the dominant source of viscous dissipation.