Experimental evaluation of forces acting on a single drop

Abstract

Adsorption of surfactants at an interface of a single drop affects the boundary condition and changes the drag force acting on the drop. However, our knowledge on the relationship between the drag force and the local interfacial forces in a contaminated system is still unsatisfactory. In this study, we measured velocity distributions in the vicinity of a single spherical drop in containing surfactants using spatiotemporal filter velocimetry (SFV) with boundary-fitted measurement region. Interfacial viscous stress, Marangoni stress and pressure distributions on an interface were evaluated from the measured velocity distributions. The drag force acting on the drop was also evaluated by integrating the stress and pressure over the interface. The results indicated that he present method is useful for understanding the relationship between the drag force and the local interfacial forces acting on a drop.