Acoustic suppression of the coffee-ring effect.
We study the influence of acoustic fields on the evaporative self-assembly of solute particles suspended inside sessile droplets of complex fluids. The self-assembly process often results in an undesirable ring-like heterogeneous residue, a phenomenon known as the coffee-ring effect. Here we show that this ring-like self-assembly can be controlled acoustically to form homogeneous disc-like or concentrated spot-like residues. The principle of our method lies in the formation of dynamic patterns of particles in acoustically excited droplets, which inhibits the evaporation-driven convective transport of particles towards the contact line. We elucidate the mechanisms of this pattern formation and also obtain conditions for the suppression of the coffee-ring effect. Our results provide a more general solution to suppress the coffee-ring effect without any physiochemical modification of the fluids, the particles or the surface, thus potentially useful in a broad range of industrial and analytical applications that require homogenous solute depositions.
Division of Biomedical Engineering, University of Glasgow, Oakfield Avenue, Glasgow, UKG12 8LT. jon.cooper@glasgow.ac.uk.
Dileep
D
Mampallil
Julien
J
Reboud
Rab
R
Wilson
Douglas
D
Wylie
David R
DR
Klug
Jonathan M
JM
Cooper
D000162:Acoustics; D012996:Solutions
D012996:Solutions