Oscillations of a water droplet on a horizontally vibrating substrate

Deformed droplets are ubiquitous in various industrial applications, such as inkjet printing, lab-on-a-chip devices, and spray cooling and can fundamentally affect the involved applications both favorably and unfavorably. Here, we employ many-body dissipative particle dynamics to investigate the oscillations of water droplets on a harmonically and horizontally vibrating, solid substrate. Three distinct scenarios of oscillations as a response to the substrate vibrations have been identified. The first scenario reflects a common situation where the droplet can follow the substrate vibrations. In the other two scenarios, favored in the case of hydrophilic substrates, droplet oscillations generate high shear rates that ultimately lead to droplet breakup. Leveraging our simulation model, the properties of the droplet and the mechanisms related to the oscillations are analyzed with a molecular-level resolution, while results are also put in the perspective of experiment. Our study suggests that the three scenarios can be distinguished by the contact-surface velocity of the oscillating droplet, with threshold velocities influenced by the substrate's wettability. Moreover, the mean magnitude of the particle velocity at the contact surface plays a key role in determining the three oscillation phases, suggesting that the capillary number of the oscillating droplet governs the phase behavior. Thus, our approach aims to optimize droplet oscillations and deformations on solid substrates, which have direct implications for technological applications.