Impact Dynamics of Aqueous Polymer Droplets on Superhydrophobic Surfaces

Controlling the impact of water droplets on nonwetting surfaces is difficult due to their superior liquid repellency. Herein, we experimentally demonstrate that the impact dynamics of water droplets on superhydrophobic surfaces can be effectively altered by adding a very small amount of high molecular weight polymer. The presence of polymer chains in water enhances droplet-surface interactions and liquid viscoelasticity, which couple with the hydrodynamic effect and thus affects the dynamic behaviors of impinging droplets. 'Whereas various impact phenomena with altered transitional boundaries in the phase diagram have been observed for droplets of aqueous polymer solutions at low concentrations, only deposition was identified for aqueous polymer droplets with high concentrations. Nevertheless, the polymer addditive does not influence droplet spreading but siginificantly slows down droplet retraction and increases the contact time of rebounding droplets on the superhydrophobic surface. Moreover, the induced non-Newtonian elongational viscosity causes strong energy dissipation, while the elasticity of polymer chains increases the restoring force during the postimpact droplet oscillation.