Abstract

Concentrating Analytes by Suppressing the Coffee Ring Effect in Extreme Conditions.

Dileep Mampallil Augustine, Post Doctoral Research Associate, University of Glasgow

[FROM SPEAKER] The coffee ring effect, the formation of heterogeneous ring-like residue when a liquid drop dries on a solid surface, is a nuisance in many applications. Previously, numerous remedies were introduced for this ill effect. However, they are not effective with hydrophilic rough surfaces where the equilibrium and receding contact angles of the drop are small. Here we show that spot-like residues can be obtained on hydrophilic surfaces like bare glass or metals with receding contact angle for water as small as 10 degrees, without any modifications of the surface or solvent chemistry. We achieve this by trapping the solute particles in acoustic standing waves formed on and in the drop. Thus we keep the drop edge clean allowing its free receding during evaporation. The resulting concentrated spot-like residue is beneficial in many applications for example, enhancing the sensitivity in bio-chemical analyses.