Self-Assembled Filament Layers in Drying Sessile Droplets: From Morphology to Electrical Conductivity

Area of Science:

• Materials Science
• Fluid Dynamics
• Nanotechnology

Background:

• Controlling filament deposition (nanowires, nanotubes) from evaporating droplets is crucial for flexible sensors and printed electronics.
• Deposit morphology significantly impacts functional properties like electrical conductivity, but remains difficult to control.

Purpose of the Study:

• To numerically investigate how filament length, stiffness, and concentration influence deposition patterns during droplet drying.
• To compare reaction-limited and diffusion-limited evaporation regimes and their effects on filament arrangement.

Main Methods:

• Numerical investigation of filament deposition during droplet evaporation.
• Comparison of reaction-limited and diffusion-limited evaporation kinetics.
• Analysis of filament length, stiffness, and concentration effects on deposition patterns.

Main Results:

• Diffusion-limited evaporation leads to the 'coffee-ring effect' and non-uniform networks.
• Reaction-limited evaporation suppresses edge accumulation, favoring centered conductive deposits.
• Filament alignment varies spatially: tangential at the contact line, radial intermediately, and random centrally.
• Longer filaments promote tangential alignment and reduce edge accumulation.
• Tuning evaporation regimes significantly lowers percolation thresholds and increases conductivity exponents.

Conclusions:

• Evaporation kinetics fundamentally alter filament arrangement and conductive network formation.
• Optimizing evaporation regimes provides guidelines for enhancing conductivity in printed electronics.
• This work quantifies the relationship between evaporation kinetics and microstructure for material design.