Molecular physics of jumping nanodroplets

Area of Science:

• Fluid dynamics
• Nanoscale phenomena
• Surface science

Background:

• Passive processes like nanodroplet jumping offer energy-efficient solutions for advanced technologies.
• Understanding droplet dynamics at the nanoscale is crucial for optimizing applications such as chip cooling and self-cleaning surfaces.

Purpose of the Study:

• To investigate the impact of thermal capillary waves and ambient gas rarefaction on nanodroplet jumping speeds.
• To quantify dissipation mechanisms governing nanodroplet jumping at experimentally challenging length scales.

Main Methods:

• High-fidelity non-equilibrium molecular dynamics simulations.
• Well-resolved volume-of-fluid continuum calculations.
• Analysis of dimensionless parameters governing nanoscale fluid behavior.

Main Results:

• Nanodroplet jumping speeds range from 0-30 m/s, significantly higher than larger droplets.
• Interfacial thermal capillary waves cause a wide statistical spread in jumping speeds.
• Reduced external drag in rarefied gas environments increases jumping speeds.

Conclusions:

• The Ohnesorge number and viscosity ratio are insufficient to describe nanoscale droplet jumping; thermal fluctuation number (Th) and Knudsen number (Kn) are essential.
• Findings are relevant for various free-surface flow processes and nanoscale applications.
• This research provides critical insights for designing next-generation cooling and self-cleaning technologies.