Capillary filling in drop merging: Dynamics of the four-phase contact point

The merging of immiscible drops differs significantly from the miscible due to formation a liquid–liquid interface between drops. immiscibility requires four-phase contact point, where drops, gas, and substrate meet. We show that this point has its own unique dynamics, never studied beforehand. For very different scenarios, propagation distance follows scales with time like t12. A model balancing driving dissipative forces agrees our experiments.