Miscibility and wettability: how interfacial tension influences droplet impact onto thin wall films

TL;DR

This study experimentally investigates how interfacial tension, influenced by miscibility and wettability, affects droplet impact dynamics on thin wall films, revealing its significant role in energy storage, crown formation, and impact behavior.

Contribution

It introduces a detailed analysis of interfacial tension effects on droplet impact, highlighting its influence on crown dynamics and energy dissipation, which was not thoroughly understood before.

Findings

Interfacial tension reduces crown extension and requires more kinetic energy for splashing.

Interfacial tension acts as a recoiling force, shortening the ascending phase.

Viscous losses dissipate nearly half of the impact energy during crown formation.

Abstract

The influence of miscibility and liquid wettability during droplet impact onto thin wall films is investigated experimentally. Despite similar liquid properties and impact conditions, differences in the splashing limit, the crown extension and the duration of the ascending phase are observed. These differences are related to the interfacial tension of the droplet/wall-film liquid pairs, which is linked to their miscibility and wettability. More precisely, by calculating the crown surface energy, we show that the energy stored in the interface between droplet and wall-film (if any) is not negligible and leads to smaller crown extensions and the need of more kinetic energy to initiate splashing. Similarly, by calculating a modified capillary time taking into account all surface and interfacial tensions, we show that the interfacial tension acts as a non-negligible recoiling force, which reduces the duration of the ascending phase. The dynamics of this ascending phase is well captured for different wall-film thicknesses if accounting for the variations of the liquid masses in movement. Overall, droplet/wall-film interactions can be seen as inertio-capillary systems where the interfacial tension between droplet and wall film plays a significant role in the storage of energy and in the crown kinetics during the impact process. Besides, this analysis highlights that viscous losses have already a significant effect during the crown extension phase, by dissipating almost half of the initial energies for droplet impact onto thin wall films, and most likely by influencing the capillary time scale through damping.