Rebound dynamics of polymer drops impacting on soft solids at low Weber numbers

Abstract

The impact of polymer drops on soft solid substrates occurs frequently in engineering applications such as inkjet printing and pesticide spraying. Here, we investigate how substrate elasticity and polymer concentration affect drop rebound at low Weber numbers. Four representative rebound metrics, including the contact time, maximum contact diameter, maximum equatorial diameter, and restitution coefficient, are analyzed. Experiments show that the rebound metrics depend only weakly on substrate elasticity, except for a modest increase in the maximum contact diameter on the ultrasoft gel. With increasing polymer concentration, the contact time increases and the maximum contact diameter decreases, whereas the maximum equatorial diameter and restitution coefficient remain nearly unchanged. Further direct numerical simulations suggest that such an increase in contact time is presumably associated with the increased solution viscosity rather than polymer elasticity. These findings advance our understanding of how substrate elasticity and drop viscoelasticity influence complex drops impacting onto compliant substrates at a low velocity.