Particle motions in sheared suspensions

The effects of diffusion out of and into drops undergoing equatorial collision in laminar shear flow were studied. With an electric field perpendicular to the direction of flow, diffusion into undeformed drops enhanced coalescence, while diffusion from the drops inhibited it. With marked outward diffusion, drops having a collision angle greater than 83° assumed a stable alignment in opposition to the velocity gradient for several minutes and then rotated to become a permanent head-on collision doublet. With inward diffusion the separation of drop centers increased along the paths of approach and the apparent angle of collision decreased. The phenomena were explained qualitatively on the basis of surface flow arising from concentration gradients at the drop surfaces. Stable multiplets were formed on collision of highly deformed drops as a result of hydrodynamic forces both with and without diffusion.