(499g) To Bounce or Not to Bounce: Impact of Viscoelastic Drops On Dry, Textured Surfaces

The deposition of aqueous drops on non-wetting surfaces is an important canonical problem for many applications, including suppressing splash or rebound of sprayed herbicides on intrinsically hydrophobic plant leaves. The addition of a small amount of high molecular weight polymer has been demonstrated to suppress drop rebound on smooth hydrophobic surfaces. The high extensional viscosity of polymer solutions and the increased viscous dissipation near the receding contact line are cited as two distinct anti-rebound mechanisms. Using drop impact experiments on micro- and nano-textured surfaces in addition to smooth hydrophobic surfaces with controlled wetting characteristics, we examine the roles of viscosity, elasticity and inertia on expansion, retraction, and rebound of well-characterized viscoelastic fluids. We show that when a viscoelastic drop impacts a textured hydrophobic surface, the answer to the question "to bounce or not to bounce" depends critically on both the fluid viscoelasticity and the surface characteristics, including details of texture and its wetting characteristics. By adopting a stick-slip flow model on textured surfaces with various topographic length scales and solid area fractions, we rationalize the dynamics leading to complete rebound following drop impact on nanotextured surfaces even for viscoelastic fluids.