Abstract
The mechanism of droplet drying is a widely concerned fundamental issue since controlling the deposition morphology of droplet has significant influence on printing, biology pattern, self-assembling and other solution-based devices fabrication. Here we reveal a striking different kinetics-controlled deposition regime beyond the ubiquitous coffee-ring effect that suspended particles tend to kinetically accumulate at the air-liquid interface and deposit uniformly. As the interface shrinkage rate exceeds the particle average diffusion rate, particles in vertical evaporation flow will be captured by the descending surface, producing surface particle jam and forming viscous quasi-solid layer, which dramatically prevents the trapped particles from being transported to drop edge and results in uniform deposition. This simple, robust drying regime will provide a versatile strategy to control the droplet deposition morphology, and a novel direction of interface assembling for fabricating superlattices and high quality photonic crystal patterns.
Highlights
The mechanism of droplet drying is a widely concerned fundamental issue since controlling the deposition morphology of droplet has significant influence on printing, biology pattern, self-assembling and other solution-based devices fabrication
More particles deposit in drop center and the areal fraction of the ring-region decreases in contrary. These results indicate that the deposition morphology could be changed by evaporation temperature
Why particles tend to deposit at center when the evaporation temperature increases? We initially deduced that the suppressed coffee-ring effect might be caused by the thermal Marangoni flow because of enlarged temperature difference between drop edge and drop apex on hot plate (Fig. S2) previous literatures have reported that the Marangoni flow is weak in water droplet[3,29], and our experiments show that deposition is more uniform in CTHC than that on the hot plate
Summary
The mechanism of droplet drying is a widely concerned fundamental issue since controlling the deposition morphology of droplet has significant influence on printing, biology pattern, self-assembling and other solution-based devices fabrication. As the interface shrinkage rate exceeds the particle average diffusion rate, particles in vertical evaporation flow will be captured by the descending surface, producing surface particle jam and forming viscous quasi-solid layer, which dramatically prevents the trapped particles from being transported to drop edge and results in uniform deposition This simple, robust drying regime will provide a versatile strategy to control the droplet deposition morphology, and a novel direction of interface assembling for fabricating superlattices and high quality photonic crystal patterns. When a drop of coffee dries on a substrate, it often leaves a ring-like stain, known as the coffee-ring effect[1] This ubiquitous phenomenon appears when the drop contact line remains pinned during the drying process; the suspended particles tend to accumulate at the drop edge for capillary outflow to replenish the local rapid solvent loss. The distinct evaporation difference between drop edge and drop center is hard to avoid, droplet usually dries at relatively slow evaporation rate that most of the suspended particles are transported to drop edge by the strong capillary outflow (Fig. 1a)
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