Impact-Driven Cavity Evolution: The Role of Miscibility in Droplet–Pool Interaction

Droplet impact on liquid films underlies applications from drug delivery and metallic quenching to inkjet printing and raindrop interactions with oil slicks. Although many involve immiscible droplet-pool systems, most prior studies have focused on miscible regimes. This work compares cavity evolution for miscible and immiscible impacts, highlighting velocity fields, and pressure distributions. At impact, both systems show similar force magnitudes, but differences in distribution and contact area drive distinct pathways. Miscible systems mix immediately, eliminating interfacial boundaries and producing near-spherical cavities governed by inertia and capillarity. Immiscible systems retain a sharp interface where interfacial tension reshapes cavity morphology, redirects forces, and induces early recirculation. Velocity analysis shows suppressed vortices in miscible cases, while immiscibility intensifies recirculation, reducing peak velocity by nearly half. Pressure fields further distinguish regimes: miscible impacts concentrate pressure at the contact point, whereas immiscible impacts spread forces, lowering peak pressure by ∼0.9 times the maximum pressure for the miscible case and generating uneven gradients that promote negative zones. These effects accelerate cavity retraction and advance Worthington jet formation. A theoretical model is proposed predicting the reduction in cavity formation time with respect to interfacial tension, predicting a reduction of 0.7 times the miscible case for the current study.