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Amplifying and attenuating the coffee-ring effect in drying sessile nanofluid droplets
1School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798.
Summary
Controlling the coffee-ring effect in nanofluid droplets is possible. Surfactants promote ring formation, while their absence leads to uniform particle coverage, explained by aggregation models.
Area of Science:
- Materials Science
- Fluid Dynamics
- Nanotechnology
Background:
- The coffee-ring effect, a phenomenon where particles deposit at the edge of a drying droplet, is common in nanofluid applications.
- Controlling particle deposition is crucial for uniform thin-film formation in various technological processes.
Purpose of the Study:
- To investigate methods for promoting or attenuating the coffee-ring effect in pinned sessile nanofluid droplets.
- To understand the underlying mechanisms governing particle distribution in drying nanofluid droplets.
Main Methods:
- Experiments involving pinned sessile droplets of water suspensions containing aluminum oxide nanoparticles.
- Addition and omission of surfactant to study its effect on droplet drying behavior.
- Development of a mathematical model based on diffusion-limited cluster-cluster aggregation.
Main Results:
- Droplets with surfactant exhibited coffee-ring formation upon drying.
- Droplets without surfactant resulted in fine, uniform particle coverage.
- Mathematical model successfully explained the difference in experimental outcomes.
Conclusions:
- Surfactant presence is a key factor in controlling the coffee-ring effect in nanofluid droplets.
- Particle sticking probability significantly influences the morphology of dried structures.
- The developed model provides insights into particle aggregation dynamics during droplet evaporation.
