CO₂-driven diffusiophoresis in an evaporating sessile droplet

Area of Science:

• Fluid dynamics
• Colloid science
• Materials science

Background:

• Controlling particle transport in evaporating droplets is crucial for thin-film deposition in printing.
• Evaporation-induced capillary flow causes the coffee-ring effect, concentrating particles at the droplet edge.
• Marangoni flow, driven by temperature or surface tension gradients, can alter particle assembly.

Purpose of the Study:

• To investigate CO2-driven diffusiophoresis as a method to control particle transport in evaporating droplets.
• To compare diffusiophoresis with capillary and Marangoni flows in different atmospheric environments (air vs. CO2).
• To understand the fundamental physics of diffusiophoresis interacting with internal droplet flows.

Main Methods:

• Utilized computational simulations to model internal flows and particle transport.
• Conducted experiments to validate the effect of diffusiophoresis on droplet deposition patterns.
• Compared particle behavior in droplets under air and CO2 atmospheres, with and without temperature gradients.

Main Results:

• CO2-driven diffusiophoresis can override capillary flow, directing particle migration based on surface charge.
• Marangoni flow can dominate diffusiophoresis under temperature gradients due to rapid ion saturation.
• Diffusiophoresis effectively modulates final particle deposition patterns, offering control over assembly.

Conclusions:

• CO2-driven diffusiophoresis provides a viable, simpler alternative for controlling particle deposition in evaporating droplets.
• This method allows for precise manipulation of particle transport with minimal solution contamination.
• The study enhances understanding of diffusiophoresis-Marangoni-capillary flow interactions in evaporating systems.