Elastocapillary Worthington jets*

The impact of droplets of viscoelastic liquids on non-wetting substrates is relevant for several deposition processes such as pesticide treatment and inkjet printing. The retraction of an impacting droplet is associated with the formation of a Worthington jet, which progressively stretches as the liquid retracts. We show that the viscoelasticity of the liquid results in a hitherto unknown elastocapillary regime in the stretching Worthington jet. We identify the impact conditions for observing elastocapillary Worthington jets, and show that these jets exhibit a linear (in time) variation of the strain rate, which can be explained by a simple theoretical model. Upon further extension, the jet exhibits beads-on-a-string structures, characteristic of elastocapillary thinning of slender viscoelastic filaments. The elastocapillary Worthington jet is not only relevant for a droplet impact on a solid substrate, but can also be expected in other configurations where a Worthington jet is observed, such as drop impact on a liquid pool and bubble bursting at an interface.