Effect of wettability on the dynamics of solid at the gas-liquid meniscus

Abstract

In this work, the effect of wettability on the dynamics of solids at a gas-liquid interface was studied experimentally and theoretically. Based on the observation of solids at a gas-liquid interface, the conventional model of floating and sinking objects was empirically analyzed, and the new mathematical model for the floating and sinking was derived to correct the conventional model under both static and dynamic conditions. To observe the effect of surface tension and change in wettability on the floating object, superhydrophobic surface was coated on the floating materials using partial combustion of hydrophobic materials. Using the introduced fabrication process, the flotation of hydrophobic solids with different physical properties was observed to test the validity of conventional models. From the experiment, the conventional model needed to be corrected to reflect the change in wettability, contact line pinning, and the existence of multiple equilibrium contact line. New mathematical model reflecting the actual physical phenomena was derived based on the experimental data. The new model showed that both buoyancy and surface tension acting on the floating object depend on the location of contact line of object, and “additional buoyancy” term exists conceptually only. Lastly, the dynamics of floating sphere entering the fluid at the gas-liquid interface was studied. By observing the free-falling spheres at the gas-liquid interface, the movement of contact line was decoupled from the movement of floating and sinking sphere. In this work, the conventional models for the floating and sinking of a sphere were tested that had been assumed to be correct for centuries, and a step was taken further to study the dynamics of floating objects. This newly proposed model would improve the understanding of forces acting on the floating objects and help to analyze natural phenomena involving the floatation of objects denser than the fluid.