Acoustic suppression of the coffee-ring effect

Area of Science:

• Fluid dynamics
• Acoustic manipulation
• Materials science

Background:

• Evaporative self-assembly of solutes in droplets commonly leads to the coffee-ring effect, a heterogeneous residue.
• This effect is undesirable in applications requiring uniform material deposition.

Purpose of the Study:

• To investigate the influence of acoustic fields on evaporative self-assembly in complex fluid droplets.
• To demonstrate acoustic control over particle self-assembly to suppress the coffee-ring effect and achieve homogeneous deposits.

Main Methods:

• Applying acoustic fields to sessile droplets containing suspended solute particles.
• Analyzing particle dynamics and pattern formation within acoustically excited droplets.
• Identifying conditions for suppressing evaporation-driven convective transport.

Main Results:

• Acoustic excitation enables control over particle self-assembly, transforming ring-like residues into homogeneous disc-like or spot-like patterns.
• Dynamic particle patterns formed under acoustic influence inhibit convective transport to the droplet contact line.
• Mechanisms of acoustic pattern formation and coffee-ring suppression were elucidated.

Conclusions:

• Acoustic fields offer a general method to suppress the coffee-ring effect without physiochemical modifications.
• This technique facilitates homogeneous solute deposition, with potential applications in various industrial and analytical fields.
• The study provides a versatile solution for controlling residue patterns in evaporating droplets.