Buoyancy-driven interactions of two deformable drops with a bulk-insoluble, nonionic surfactant are studied with a curvatureless boundary-integral algorithm. At moderate drop-to-medium viscosity ratios with a linear equation of state, the surfactant causes breakup of the larger drop to become dominant over breakup of the smaller drop at O (0.1) values of the dimensionless gas constant β for a surface Péclet number P es of 100. For P es ≤ 10, the surfactant has little effect on breakup for β ≤ 0.2. For P es = 1000, critical horizontal offsets for breakup of the larger drop exceed those for breakup of the smaller drop at β = O (0.01). The influence of surfactant on the deformation and breakup of the smaller drop increases when it becomes closer in size to that of the larger drop. Surfactant effects are less significant when the drop-to-medium viscosity ratio is greater than unity. For the case of bubbles, at P es = 100, the surfactant is swept to the trailing edges early in the trajectories and leads to cusp formation at β = O (0.01).
|Original language||English (US)|
|Number of pages||11|
|Journal||Colloids and Surfaces A: Physicochemical and Engineering Aspects|
|State||Published - Jul 20 2006|
Bibliographical noteFunding Information:
MAR is grateful to the VDIL at UMD and the University of Minnesota Supercomputing Institute for computing resources. This work was supported by NASA grants NAG3-2116 and NNCO5GA55G, and grant 40430-AC from the Petroleum Research Fund of the American Chemical Society.