Patterning in colloidal droplets by forced airflow

Abstract

Strategies to suppress the coffee-ring effect are critical in various applications, such as printing, surface manufacturing, and biochemical analysis. We propose a simple and contactless method based on forced airflow to obtain uniform depositions of drying colloidal droplets in this work. This method eliminates the coffee-ring effect without chemical/physical modifications of the suspensions and substrates. The tangential liquid flow in the drying droplets caused by forced airflow prevents nanoparticles from accumulating on the periphery and diminishes the three-phase contact line's pinning. The contact line retracts continuously and smoothly, resulting in a relatively uniform stain pattern. This paper experimentally explores several critical parameters in this strategy, including the droplet volume, the distance between droplets and the air inlet pipe, and forced airflow velocity. Our comprehensive study of the forced-air strategy offers potential for further diverse applications in both industrial and scientific fields.