The effect of polymers on the retraction of impacting droplets.

Viscoelastic properties can drastically change the dynamics of droplets impacting a hydrophobic surface. While long polymers in aqueous drops have no effect on drop spreading, the retraction speed of dilute polymer solutions can be up to two orders of magnitude slower. Since the discovery of this phenomenon more than two decades ago, the mechanism governing this slower retraction speed has been up for debate. Latest insights point towards interactions between the polymer molecules and the substrate, but a prediction for the retraction velocity based on the fluid and substrate properties is still lacking.

 

We revisited the viscoelastic drop retraction problem and found two different modes of retraction for dilute polymer solutions. Additionally, evaporation of the droplet before impact was found to be of great influence on the retraction dynamics.