The impact of single and clouds of drops on a solid surface tions, e.g., as in the deformation and breakup of drops in extensional is of great scientific interest and practical importance. An flows under conditions of Stokes flow (Stone, H. A., and Leal, L. G., improved understanding of drop impact is needed in applica-J. Fluid Mech. 220, 161 (1990)) (19) and the formation of drops tions as diverse as spray coating, spray painting, delivery of from capillaries (Zhang, X., and Basaran, O. A., Phys. Fluids 7, 1184 agricultural chemicals, spray cooling, ink-jet printing, soil (1995)) (20) has shown that dynamic surface tension (DST) effects erosion due to rain-drop impact, and turbine wear (see, e.g., can radically alter the dynamics compared to situations in which the fluid interface is clean. In this paper, we present results of an the review article by Rein ( 1)). Even in the absence of experimental study that examines the impact with a solid substrate such phenomena as evaporation, cooling, solidification, and of drops of Newtonian liquids containing two commonly used surfacchemical reactions, the dynamics of drop impact is a formitants. In the experiments, an ultra high-speed video and associated dable free boundary problem. Motivated by the spraying image analysis system is used to monitor the dynamics of the impact of agricultural chemicals onto crops and spray coating and process. On account of the extremely large deformations that a drop painting, the findings of an experimental study are presented exhibits and the large-amplitude oscillations that it undergoes upon in this paper in which the drops impacting a surface are not impacting and spreading on the substrate, DST plays a complex and pure liquids but aqueous solutions containing surfactants.
dominant role in determining the dynamics and the asymptotic state
In a typical application, a nearly spherical drop is launched that is approached at large times. A major consequence of the prestoward a solid surface and impacts it with a large velocity, ence of surfactant is that on the one hand its accumulation on the as shown in Fig. 1(a) for a water drop at the instant when fluid interface reduces the surface tension and thereby enhances the spreading of the drop across the substrate. On the other hand, the it has just impacted a glass substrate. Upon impact, the initial non-uniform distribution of surfactant along the fluid interface gives drop momentum that is in the direction normal to the subrise to Marangoni stresses that inhibit drop spreading. Given the fact strate gives rise to a radial flow along the surface. As shown that many liquids used in atomization coating applications ranging in Fig. 1(b)-(c), this results in the drop spreading rapidly from the spraying of agricultural chemicals to painting of substrates in the form of a liquid disc on the substrate. If the initial contain surfactants and/or other surface-active species, the fundakinetic energy (inertial force) is much larger than the surface mental results to be reported in this paper have important practical energy (surface tension force), the drop can ''splash'' by ramifications.