The control of dry-out patterns using bubble-containing droplets.

Area of Science:

• Fluid dynamics
• Nanomaterials science
• Surface science

Background:

• Evaporation of droplets containing nanoparticles is crucial for self-assembly.
• Understanding droplet behavior during evaporation is key to controlling deposit patterns.

Purpose of the Study:

• To investigate how internal bubbles influence the dry-out patterns of evaporating nanofluid droplets.
• To determine if bubble characteristics can be used to tune the morphology of deposit patterns.

Main Methods:

• Introducing bubbles of varying diameters and lifetimes into nanofluid droplets.
• Systematically altering nanoparticle properties (type, size, concentration, shape, wettability).
• Measuring the geometric dimensions of the resulting dry-out patterns.

Main Results:

• A long-lifetime bubble leads to a complete ring-like deposit.
• Ring diameter and thickness are dependent on bubble base diameter.
• Ring completeness decreases with shorter bubble lifetimes.
• Particle pinning of the contact line near the bubble perimeter drives ring formation.

Conclusions:

• Bubble presence and characteristics are primary determinants of dry-out patterns in evaporating nanofluid droplets.
• This study presents a simple, cost-effective method to produce and control ring-like deposits.
• The findings are applicable to various evaporative self-assembly applications.