## 1 Introduction
### Morphological Considerations on the Hydrodynamics of Splashing
In addition, a higher viscosity leads to an increase of the damping forces involved in the morphological development of splash, delaying both prompt and crown types. Therefore, while viscosity promotes splash after drop impact on dry surfaces, in the presence of thin liquid films, its role reverts. Lastly, high surface tension inhibits splashing both for dry or wetted surfaces. Over the years, researchers wanted to produce thinner liquid films and study these particular impacts. For example, [PERSON] and [PERSON] [20] did experiments centered on the splashing of a single droplet upon very thin liquid films (\(\delta<0.1\)). They confirmed that the critical Weber number and the splashing dynamics remain influenced by the thickness of the liquid film. However, the authors also noticed that the critical Weber number converges to a minimum value as \(\delta\) decreases, which depends on the fluid viscosity and surface characteristics underneath the liquid film. In the study of drop impact on wetted surfaces, it is important to understand whether the surface underneath the liquid film influences the outcome. With that in mind, [PERSON] et al. [21] combined the influence of a rough surface and a thin liquid film upon the splashing limit and dynamics. They recognized that both cases substantially changed the splashing limit and dynamic. A rough surface decreased the critical Weber number drastically for the transition to splash, and the surface topography overtakes the importance of other governing parameters, especially in the splashing regime. For example, considerable differences in the surface tension and viscosity became less significant and made the outcome of impact very similar. The splashing behavior of a rough surface covered by a thin liquid film was a combination of both cases. Boundaries between the different impact regimes are common and widely reported. [PERSON] et al. [22] synthesized several empirical correlations in the literature which established boundaries between the different impact regimes and classified them as very distinct. The main differences were due to the distinct impact conditions which originated them. Concerning the effect of fluid properties, [PERSON] et al. [23] centered their work on the numerical simulation of a droplet impinging upon films and remarked that while surface tension and viscosity decreases, more momentum is imparted on the crown development, increasing its height and decreasing its thickness. In the same way, the formation of prompt splashing is enhanced by the decrease in surface tension and viscosity of the fluid. They found that Weber number plays a more important role in droplet impact behavior than the Reynolds number. Increasing the Weber number accelerates the impact process and increases the number of splashing droplets. Other studies concern droplet impacts upon immiscible liquid films (e.g., water and oil), such as the work performed by [PERSON] and [PERSON] [24]. Immiscibility induces completely different hydrodynamic behaviors. A water droplet impinging on an oil film creates a compound crown, followed by the formation of a central jet; contrarily, an oil droplet impinging on a water film causes quick spreading. They also studied the influences of some parameters, such as the Weber and Ohnesorge numbers, the viscosity ratio, and the dimensionless thickness of the liquid film. Namely, concerning the last parameter, thicker films show a behavior similar to miscible liquids, with the timescales delayed relative to thinner liquid films. Recently, [PERSON] and [PERSON] [25] studied the droplet splashing on a thin moving film only for high Weber number (\(We>2281\)). They reported that the liquid film velocity affects the crown geometry considerably. The high inertial force of the droplet enlarges the expansion of the crown, which causes a larger diameter.