Particle dynamics near fluid interfaces in low-Reynolds number flows

Numerical solutions for the creeping motion of a spherical particle in a linear axisymmetric straining flow normal to a deformable interface are presented for a range of viscosity ratios, capillary numbers and Bond numbers. The parameter ranges investigated have applications in areas of flotation (small interface deformation) and material processing (large interface deformation). The accuracy of previous solutions for flotation problems, which neglect interface deformation is considered, along with the magnitude and form of interface deformation "defects" that may appear in material processing applications involving fluids containing bubbles or small particles.; Numerical solutions for the equilibrium particle-interface configuration for a neutrally buoyant spherical particle contacting a deformable fluid/gas interface in a linear axisymmetric straining flow at low Reynolds number are presented for a range of contact angles and capillary numbers. These solutions may have applications both in flotation separation processes and in contact angle and surface tension measurement. In addition, the accuracy of simply combining previous results for particle detachment due to particle buoyancy with the results for particle detachment due to viscous forces is considered. The equilibrium configuration is especially sensitive to the inclusion of a small amount of flow for small contact angles and for capillary numbers near the critical capillary number.; Trajectories of small spherical particles around a spherical drop (bubble and solid) are calculated from an approximate solution employing a matched asymptotic expansion. Viscous interaction is seen to have a large effect on the trajectory around a solid collector and a small effect on the trajectory around a bubble. Previous solutions are found to be in error in their prediction of an increase in the capture efficiency because of viscous interactions; the capture efficiency decreases significantly in this case.; Finally, the trajectories of particles around bubbles and the capture of particles by bubbles is investigated experimentally.