Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

Area of Science:

• Fluid dynamics
• Thermodynamics
• Surface science

Background:

• Droplet motion is crucial in various applications, including microfluidics and heat transfer.
• Traditional droplet manipulation often relies on wettability gradients.
• Understanding droplet behavior at the nanoscale, particularly at the contact line, is essential.

Purpose of the Study:

• To investigate droplet motion driven by thermal singularity on heated or cooled substrates.
• To analyze the role of thermal singularity in altering contact angles.
• To develop a model explaining droplet movement induced by thermal gradients.

Main Methods:

• Numerical simulation using a continuum model for one-component liquid-gas hydrodynamics.
• Physical analysis of droplet motion down to the contact line scale.
• Comparison with droplet motion induced by wettability gradients.

Main Results:

• Thermal singularity at the contact line suppresses the Marangoni effect.
• Evaporation/condensation near the contact line increases contact angle with substrate temperature.
• Droplet motion is achieved by exploiting temperature-dependent contact angle changes.
• A simple fluid dynamical model explains droplet motion at the macroscale.

Conclusions:

• Droplet motion can be controlled by thermal gradients via contact angle modulation.
• This thermal gradient-driven motion is distinct from wettability gradient-driven motion.
• The flow field at the droplet scale is independent of contact line dynamics.