Characterization of aggregation and declustering tendency of hydrophobic fine particles in water

When hydrophobic particles are added to water, they form clusters by interparticle gas bridging. The hydrostatic, capillary and buoyancy forces acting on the submerged clusters can gradually mobilize the interparticle gas bubbles. As particles are released from the cluster gradually, the cluster is transformed into slurry state. We studied the clustering and declustering characteristics of hydrophobic granular particles (dyed quartz sand with 0.33 mm and 0.73 mm in diameter), which were applied to the water surface and submerged after forming clusters. Behavior of the particle clusters was evaluated to characterize (1) clustering tendency of particles, and (2) gradual particle declustering by mobilization, coalescence and release of air bubbles from the submerged cluster. Cluster formation and declustering rates of the particles were evaluated based on the experimental data and observations. Clustering tendency of the particles depends on the surface tension characteristics (or spreading tendency) of the particles on the water surface. On the other hand, stability of the submerged cluster is highly dependent on the surface roughness which we propose affects the ability of the microbubbles to coalesce within the submerged cluster. Particle cohesion coefficient for clustering tendency and particle declustering rate for transformation of the submerged aggregate to slurry state were estimated from experimental data.