Lateral jetting during off-center drop collisions on substrates

In this work, we experimentally study the behavior of a sessile water drop impacted by another drop of water using a bottom-up viewing configuration and optically clear substrates. By varying the Weber number and the center-line impact offset distance, a variety of regimes based on the post-impact geometry are observed. A pair of side lobes/jets extending more than twice the maximum spread of the impacting drop are found to form at low to moderate Weber number at an offset distance close to three-quarter the combined radii of the two initial drops. The onset of these jets is probed further with a high-speed imaging study showing slender jets issue from the impacting drops ∼0.25 ms after impact at a velocity an order of magnitude greater than the impact velocity.