  We study the effect of insoluble surfactants on the impact of surfactant-free
droplets on surfactant-laden thin liquid films via a fully three-dimensional
direct numerical simulations approach that employs a hybrid
interface-tracking/level-set method, and by taking into account
surfactant-induced Marangoni stresses due to gradients in interfacial
surfactant concentration. Our numerical predictions for the temporal evolution
of the surfactant-free crown are validated against the experimental work by Che
and Matar (2017). We focus on the crown-splash regime, and we observe that the
crown dynamics evolves through various stages: from the the growth of linear
modes (through a Rayleigh- Plateau instability) to the development of
nonlinearities leading to primary and secondary breakup events (through droplet
shedding modulated by an end-pinching mechanism). We show that the addition of
surfactants does not affect the wave selection via the Rayleigh-Plateau
instability. However, the presence of surfactants plays a key role in the late
stages of the dynamics as soon as the ligaments are driven out from the rim.
Surfactant-induced Marangoni stresses delay the end-pinching mechanisms to
result in longer ligaments prior to their capillary singularity, while also
promoting the spanwise merging between ligaments. Finally, we show that the
addition of surfactants leads to surface rigidification and consequently to the
retardation of the flow dynamics.
