Interaction of a spherical particle with a neutrally buoyant immiscible droplet in salt solution

The interaction of rigid spherical particles with liquid interfaces (e.g., air/water or oil/water) underpins important industrial applications such as the separation of minerals in flotation. The object of this work was to investigate experimentally and theoretically the impact of surface properties of the particle (in terms of wettability) on the attachment behaviours to the oil/water (O/W) interface. Towards this aim, we constructed an experimental setup with which the interaction between particles and an oil droplet (aniline) were directly observed using high speed digital camera. An individual aniline droplet was made to be neutrally buoyant in salt solution. The interaction was manipulated through variations in particle surface hydrophobicity. This method allowed to capture three different interaction regions: (I) approaching particle at large separation distance; (II) collision accompanied by rebound, and (III) liquid film thinning, rupture followed by the three-phase contact (TPC) formation including a dynamic movement of the TPC line. The results showed that particle-droplet attachment was mainly dependent on the hydrophobicity/wettability of the solid particles. In addition, a numerical model based on the Discrete Element Method (DEM) was presented implementing an interface distortion dependent capillary force model which showed fairly good agreement with the experiments