Transient flow induced by the adsorption of particles

The paper describes the physics of particle adsorption and the spontaneous dispersion of powders that occurs when they come in contact with a fluid-liquid interface. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. Our PIV measurements show that the adsorption of a spherical particle at the interface causes an axisymmetric streaming flow about the vertical line passing through the particle center. The fluid directly below the particle rises upward, and near the surface, it moves away from the particle. The flow, which develops within a fraction of second after the adsorption of the particle, persists for several seconds. The flow strength, and the volume over which it extends, decrease with decreasing particle size. The streaming flow induced by the adsorption of two or more particles is a combination of the flows which they induce individually. The flow not only causes particles sprinkled together onto a liquid surface to disperse, but also causes a hydrodynamic stress which is extensional in the direction tangential to the interface and compressive in the normal direction. These stresses can cause the breakup of particle agglomerates when they are adsorbed on a liquid surface.