Confined colloidal droplets dry to form circular mazes.

Area of Science:

• Fluid dynamics
• Materials science
• Physical chemistry

Background:

• Sessile droplets containing particles typically form coffee-stain rings upon drying due to evaporative flux and particle deposition.
• Understanding droplet evaporation is crucial for various applications, including printing, coating, and biological sample preparation.

Purpose of the Study:

• To investigate the drying behavior of particle-laden droplets confined within a slit.
• To identify novel pattern formation mechanisms beyond the typical coffee-stain ring.

Main Methods:

• Experimental observation of droplet evaporation under controlled confinement and slow evaporation rates.
• Analysis of the resulting deposit patterns and correlation with evaporation dynamics.

Main Results:

• Particle-laden droplets confined in a slit and evaporating slowly do not form coffee-stain rings.
• Intricate, circular maze-like patterns are formed instead of uniform rings.
• The formation of these maze patterns is dependent on specific confinement and evaporation conditions.

Conclusions:

• Confinement and slow evaporation fundamentally alter droplet drying behavior, suppressing coffee-stain ring formation.
• Novel maze-like patterns emerge from confined droplet evaporation, presenting new avenues for pattern formation research.
• These findings suggest potential for controlled fabrication of complex microstructures using droplet evaporation.