Impact of drops of dilute polymer solutions

We revisit, with new experiments and new theory, the old problem of aqueous drop deposition on hydrophobic surfaces. It is well known that dilute high molecular weight polymers when added to water improve the deposition by preventing rebound of the drops. This occurs because the retraction of the contact line of the drop is slowed down by the presence of polymers, which has been explained in terms of the polymer elasticity adding an extra elastic force that slows down retraction. However other people argue that polymer adsorption onto the hydrophobic surface is the main mechanism behind the slowing down of the contact line. Our new experiments suggest that both effects may actually come into play, depending on polymer concentration and environmental factors such as evaporation. We present a complementary study of the moving contact line of polymeric drops that reveal the underlying mechanisms.