The aim of this paper is to study the mechanism by which clumps of some powdered materials break up and disperse on a liquid surface to form a monolayer of particles. We show that a clump breaks up because when particles on its outer periphery come in contact with the liquid surface they are pulled into the interface by the vertical component of capillary force overcoming the cohesive forces which keep them attached, and then these particles move away from the clump. In some cases, the clump itself is broken into smaller pieces and then these smaller pieces break apart by the aforementioned mechanism. The newly-adsorbed particles move away from the clump, and each other, because when particles are adsorbed on a liquid surface they cause a flow on the interface away from themselves. This flow may also cause particles newly-exposed on the outer periphery of the clump to break away. Interestingly, when many particles asymmetrically break away from a clump, the clump itself is pushed in the opposite direction by the flow caused by the newly-adsorbed particles. Since millimeter-sized clumps can breakup and spread on a liquid surface within a few seconds, their behavior appears to be similar to that of some liquid drops which can spontaneously spread on solid surfaces. However, if the capillary force is not large enough to overcome the cohesive force holding the clump together, the clump may not breakup.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fluid-fluid interfaces
- Interfacial tension
- Particle clumps