Dynamics and disintegration of drops of polymeric liquids

The deformation and the disintegration of drops of polymer solution upon impact with solid obstacles are investigated both experimentally and theoretically. High molecular polyethylene oxide (PEO) and polyacrylamide (PAM) solutions at concentrations 1-10,000 ppm, as well as pure water and glycerine, are used as tested liquids. A feature of this work is the use of a non-standard hydrodynamic situation, namely the collision of a spherical drop with a small disk-like solid target. In the experiments, a drop of 3 mm diameter collides with a 4 mm disk target with velocity of 3.4 m/s. If water is used, upon impact the drop is transformed into a liquid lamella (i.e. a circular film with a rather thick toroidal rim). The lamella increases in diameter and then it retracts with ejection from the rim of a set of radially directed secondary jets that, in turn, break up into secondary droplets. Typically polymeric additives do not influence much the growth and the retraction rate, but they drastically modify the disintegration process. Depending on the polymer nature and its concentration, four regimes of drop impact are observed: (i) the secondary jets are transformed into capillary thinning filaments partially retarding the detachment of secondary drops, (ii) the elastic stresses in the thinning filaments force all secondary droplets to move back to the target suppressing splashing, (iii) no rim instabilities are developed and lamella with smooth rim is formed and (iv) no lamella formation. Criteria of transition from one to another regime of drop impact are proposed.