Air bubble-triggered suppression of the coffee-ring effect

Abstract

Developing simple methods to suppress the coffee-ring effect without modifying colloidal suspensions (e.g., inherent properties of the solute or solvent) is critical for related industrial and bio-medical applications. This study experimentally investigates adding air bubbles in droplets as a means of suppressing the coffee-ring effect. The added air bubbles induce a concave meniscus and an increased receding contact angle, resulting in fast and smooth retreating of the three-phase contact line and a relatively uniform stain pattern. This method can be employed to droplets at a volume ranging from 2.5 μL to 0.1 mL. These findings can be easily exploited to modulate the drying process and the morphology of stain patterns, with potential applications in scientific and industrial fields.