Effect of Polymer Additives on the Wetting of Impacting Droplets

Abstract

When a droplet of water impacts a hydrophobic surface, the drop is often observed to bounce. However, for about 10 years it has been known that the addition of very small quantities (approximately 100 ppm) of a flexible polymer such as poly-(ethylene oxide) can completely prevent rebound. This effect has for some time been explained in terms of the stretching of polymer chains by a velocity gradient in the fluid, resulting in a transient increase in the so-called "extensional viscosity." Here we show, by measuring the fluid velocity inside the impacting drop, that the extensional viscosity plays no role in the antirebound phenomenon. Using fluorescently labeled lambda DNA we demonstrate that the observed effect is due to the stretching of polymer molecules as the droplet edge sweeps the substrate, retarding the movement of the receding contact line.

Comparison of spontaneous wetting and drop impact dynamics of aqueous surfactant solutions on hydrophobic polypropylene surfaces: scaling of the contact radius

“…7). This tells that surfactant influences the impact process of water drops, similarly as some polymers do [48][49][50], and reduce the oscillations by providing an additional dissipation channel. So, the impact process is shortened and capillarity-driven spreading of the drop can start soon after.…”

Dynamic contact angle of dilute polymer solution drops impacting on a hydrophobic surface

“…Even in the case of very dilute solutions, comparison with the Newtonian solvent (e.g., water) reveals significant differences in the behaviour of the moving contact line during the spreading and/or receding phase, in the amplitude of the dynamic contact angle, as well as in the intrinsic time of the phenomenon [19][20][21]. A well-known example is the so-called anti-rebound effect of polymer additives: When a droplet of water falls on to a hydrophobic surface, such as the waxy leaf of a plant, the drop is often observed to bounce off, however the addition of very small quantities (∼100 ppm) of a flexible polymer can completely prevent rebound, by reducing the recoil velocity of the drop after the inertial spreading of two orders of magnitude [22,23].…”

Mechanical vibrations of magnetically levitated viscoelastic droplets

“…Additives such as polymers and small particles can have a dramatic effect on the surface and rheological properties of small liquid droplets. These can, in turn, influence properties such as the wetting, spreading and dewetting behaviour of the fluids [3][4][5][6] . They also have a significant influence on their performance in applications such as droplet atomisation, ink jet printing, fuel injection 7 , microscale mixing/demixing 8,9 , and during drop impact and rebound phenomena 6 .…”

“…These can, in turn, influence properties such as the wetting, spreading and dewetting behaviour of the fluids [3][4][5][6] . They also have a significant influence on their performance in applications such as droplet atomisation, ink jet printing, fuel injection 7 , microscale mixing/demixing 8,9 , and during drop impact and rebound phenomena 6 . Viscoelastic vibrational modes may also influence the dynamical properties of atomic nuclei 10 , crustal deformation of planets 11,12 and energy relaxation mechanisms in neutron stars 13 .…”