Thin three-dimensional droplets on an oscillating substrate with contact angle hysteresis

Area of Science:

• Fluid dynamics
• Soft matter physics

Background:

• Recent experiments demonstrate uphill droplet motion on inclined planes driven by vertical oscillations.
• This phenomenon challenges conventional understanding of fluid behavior under external forces.

Purpose of the Study:

• To investigate the mechanism behind counterintuitive uphill droplet motion induced by vertical oscillations.
• To develop a simplified model focusing on dominant forces like acceleration, gravity, and surface tension.

Main Methods:

• Utilized a theoretical model neglecting liquid inertia and viscosity.
• Analyzed droplet motion by separating it into spreading and swaying modes.
• Investigated the role of contact line laws and contact angle hysteresis.

Main Results:

• Droplet motion is governed by the interplay of spreading and swaying modes.
• Maximum rise velocity is achieved when these modes are in phase.
• Contact angle hysteresis can synchronize out-of-phase modes, enhancing uphill climbing.

Conclusions:

• The model explains uphill droplet motion through mode synchronization.
• Contact angle hysteresis plays a crucial role in enabling or enhancing climbing.
• The findings provide insights into droplet dynamics under oscillatory forcing.