ABSTRACT
We study dense and highly polydisperse emulsions at droplet volume fractions Ï≥0.65. We apply oscillatory shear and observe droplet motion using confocal microscopy. The presence of droplets with sizes several times the mean size dramatically changes the motion of smaller droplets. Both affine and nonaffine droplet motions are observed, with the more nonaffine motion exhibited by the smaller droplets which are pushed around by the larger droplets. Droplet motions are correlated over length scales from one to four times the mean droplet diameter, with larger length scales corresponding to higher strain amplitudes (up to strains of about 6%).
ABSTRACT
Experiments are performed on the transport of gas and liquid in a column of aqueous foam maintained in steady state by a constant gas flux at the bottom. We measure vertical profiles of the bubble velocities, the bubble radii, and the liquid fraction, for four different gas fluxes. In steady state the bubbles move upwards with constant speed equal to the measured gas flux, which accounts for all transport of gas. The bubbles also coarsen by gas diffusion at a rate that depends on liquid fraction. Away from the bottom, the Plateau border radii are constant. Therefore capillary effects are negligible and the steady-state liquid-fraction profile is set chiefly by the balance of viscous forces and gravity. The flow within the Plateau borders may be modeled with a no-slip boundary condition for our system. These findings provide a simple description of steady-state foams via the coarsening and drainage equations, which can be combined and solved analytically for bubble radius and liquid-fraction profiles.
