Elastocapillary Worthington jets in viscoelastic liquids*

The impact of droplets of viscoelastic liquids on non-wetting substrates is relevant for various deposition processes such as spray cooling, spraying pesticides, and inkjet printing. The retraction of an impacting droplet on a non-wettable substrate is often associated with the formation of a Worthington jet, which is fed by the retracting liquid. Here, we investigate the critical role of viscoelasticity in a characteristic transition from an inertiocapillary to an elastocapillary regime in the stretching Worthington jet. To achieve this, we perform drop impact experiments on non-wetting solid surfaces for identifying the impacting conditions with respect to the inertia and elasticity effects, revealing that viscoelasticity results in a pinned contact line on the non-wettable substrate. In addition, we confirm via numerical simulations using the open-source Volume-Of-Fluid code Basilisk (with adaptively-refined grid to capture the interface) that pinning conditions on the substrate are key for the development of beads-on-the-string structures, characteristic of the elastocapillary thinning of slender viscoelastic liquid filaments.