Study of grid-structured flotation particle surface wetting behavior characteristics

Difference of mineral particles in surface wettability is the key to success of flotation process, and the wetting characteristics are influenced by both surface chemical properties and physical morphological structure. In order to further clarify the influence of surface physical morphology on wetting behavior, five groove-structured surfaces with different roughness coefficients and percentages of surface area are prepared with polydimethysiloxane sheet (PDMS) as material and through photo-engraving process. Then the wetting behavior of droplets on PDMS surface is explored using self-made dynamic/static contact angle measuring system and the three-phase contact line movement testing system. As indicated by both dynamic and static contact angle measurements, when the surface roughness remains unchanged, the contact angles in different wetting directions on groove-structure surface all tend to decrease with the increase of surface area, and when the percentages of surface area are identical, the contact angles in different wetting directions are positively correlated with roughness of solid surface; the dynamic and static contact angles of droplets in the direction perpendicular to the grooves on the surfaces of different specimens are all greater than those in the parallel direction (i.e.θ_⊥ > θ_∥), and the difference in values of contact angles in different wetting directions tends to decrease with the increased wettability of solid surface. Results of test on dynamic contact angles also indicate that the hysteresis of contact angels (Δθ = θ_a − θ_r) is positively correlated with percentage of surface area and negatively correlated with surface roughness, and the predicted values of both forward and receding contact angles are basically in agreement with the actually measured values, indicating that the dynamic contact angels of droplets can truly reflect the change in surface wettability; and the droplet when rolling is observed to always undergo a cyclic motion on different structured solid surfaces, namely, its rear-end contact line first separate from the solid surface and then adhere onto the latter to form a front-end contact line. As shown by results of test on three-phase contact line, the droplets are more inclined to move first along the grooves and in this case a better wetting and dewatering effect can be expected than in the case when the droplets travel across the grooves as the wetting radius of each droplet is much reduced under the pinning effect of the microstructure of solid surface; the three-phase contact line moves on the groove-structured surface intermittently in a cyclical process of depinned−pinned−deppinned−pinned. The work made in the paper sheds more light on the effect of physical morphological structure of surface mineral particles on characteristics of wetting behavior, which provides a certain theoretical support for the follow-up research work in this field.