Cohesive oil droplets as an ideal model granular system

Abstract

The research presented in this thesis contains experiments focusing on the effect of cohesion in a model emulsion system. The projects explore the combined role of buoyancy and cohesion in two-dimensional geometries. In the first study, we develop a simple method to measure the cohesive force due to depletion. By utilizing a force balance between the buoyant force and cohesive force and slowly increasing the buoyant force we can find the critical force where two droplets break apart. In the second study, the spreading of oil droplets is investigated. Interestingly, the pile of droplets could be described through an analogy with a continuum system rather than a granular system. It was found that a cohesive length scale, analogous to the capillary length in liquids, which is defined through a balance of the buoyant force and the cohesive strength could describe the spreading of the pile. In the third study, the flow of oil droplets through a two-dimensional hopper is investigated. In cohesionless systems, clogging can be described by the dimensionless ratio of the hopper opening to the particle diameter. We demonstrated that this ratio was insufficient in describing our cohesive system and that a cohesive length scale was required to describe the clogging behaviour of our system.