  Droplet deposition after impact on superhydrophobic surfaces has been an
important area of study in recent years due to its potential application in
reduction of pesticides usage. Minute amounts of long chain polymers added to
water has been known to arrest the droplet rebound effect on superhydrophobic
surfaces. Previous studies have attributed different reasons like extensional
viscosity, dominance of elastic stresses or slowing down of contact line in
retraction phase due to stretching of polymer chains. The present study
attempts to unravel the existence of critical criteria of polymer concentration
and impact velocity on the inhibition of droplet rebound. The impact velocity
will indirectly influence the shear rate during the retraction phase, and the
polymer concentration dictates the relaxation timescale of the elastic fluids.
Finally we show that the Weissenberg number (at onset of retraction), which
quantifies both the elastic effects of polymer chains and the hydrodynamics, is
the critical parameter in determining the regime of onset of rebound
suppression, and that there exists a critical value which determines the onset
of bounce arrest. The previous three causes, which are manifestations of
elastic effects in non-Newtonian fluids, can be related with the proposed
Weissenberg number criterion.
