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Rate-dependent interface capture beyond the coffee-ring effect.

Li Y, Yang Q, Li M, Song Y - Sci Rep (2016)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences (ICCAS), Beijing Engineering Research Center of Nanomaterials for Green Printing Technology, Beijing National Laboratory for Molecular Sciences (BNLMS), Beijing, 100190, P. R. China.

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.

No MeSH data available.


Two regimes of drying process controlled by evaporation kinetics.(a,b) Obvious capillary outflow (streamlines in snapshot a) transport the suspended particles to drop edge at low evaporation temperature (T = 30 °C), forming ring stains (schematic b). (c,d) Iridescence on drop surface at high temperature (T = 70 °C, arrowed in c) indicates the assembling of on drop surface by an collection process, forming uniform deposition (schematic d). Particles near surface (shaded particles in the gray area in d left) are captured by the rapid descending surface with only a tiny part been transported to drop edge. The thickness of the outflow arrows schematic the relative intensity. The scale bar, 0.5 mm in (a,c).
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f2: Two regimes of drying process controlled by evaporation kinetics.(a,b) Obvious capillary outflow (streamlines in snapshot a) transport the suspended particles to drop edge at low evaporation temperature (T = 30 °C), forming ring stains (schematic b). (c,d) Iridescence on drop surface at high temperature (T = 70 °C, arrowed in c) indicates the assembling of on drop surface by an collection process, forming uniform deposition (schematic d). Particles near surface (shaded particles in the gray area in d left) are captured by the rapid descending surface with only a tiny part been transported to drop edge. The thickness of the outflow arrows schematic the relative intensity. The scale bar, 0.5 mm in (a,c).

Mentions: 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) However, previous literatures have reported that the Marangoni flow is weak in water droplet329, and our experiments show that deposition is more uniform in CTHC than that on the hot plate (Figs S3 and S4, Mov. S3, S4), which indicates the temperature caused Marangoni flow has weak influence on the deposition morphology. To further reveal the mechanism, we use stereomicroscope to investigate different drying behaviors of droplets with pinned contact line (Mov. S1, S2). When a drop dries at near room temperature (30 °C), obvious outflow induces edge growth process and forms ring-like fashion (Fig. 2a,b). In contrast, a drop drying on heated substrate (70 °C) shows quite inconspicuous growth of the ring region. Interestingly, some angle-dependent iridescence emerges on the surface, which is absence at low temperature (Fig. 2c). This iridescence lasts long until the end of the drying process, and it appears earlier when increasing the substrate temperature. As no pigment was added, we will find that this luster comes from the structure color of ordered assembling of the suspended monodispersed polystyrene particles on drop surface, like color and luster of opal30. This surface assembling process produces increased surface viscosity that is much larger than the bulk4, preventing the suspended particles at air-water interface from moving to the contact line (Fig. 2d).


Rate-dependent interface capture beyond the coffee-ring effect.

Li Y, Yang Q, Li M, Song Y - Sci Rep (2016)

Two regimes of drying process controlled by evaporation kinetics.(a,b) Obvious capillary outflow (streamlines in snapshot a) transport the suspended particles to drop edge at low evaporation temperature (T = 30 °C), forming ring stains (schematic b). (c,d) Iridescence on drop surface at high temperature (T = 70 °C, arrowed in c) indicates the assembling of on drop surface by an collection process, forming uniform deposition (schematic d). Particles near surface (shaded particles in the gray area in d left) are captured by the rapid descending surface with only a tiny part been transported to drop edge. The thickness of the outflow arrows schematic the relative intensity. The scale bar, 0.5 mm in (a,c).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835725&req=5

f2: Two regimes of drying process controlled by evaporation kinetics.(a,b) Obvious capillary outflow (streamlines in snapshot a) transport the suspended particles to drop edge at low evaporation temperature (T = 30 °C), forming ring stains (schematic b). (c,d) Iridescence on drop surface at high temperature (T = 70 °C, arrowed in c) indicates the assembling of on drop surface by an collection process, forming uniform deposition (schematic d). Particles near surface (shaded particles in the gray area in d left) are captured by the rapid descending surface with only a tiny part been transported to drop edge. The thickness of the outflow arrows schematic the relative intensity. The scale bar, 0.5 mm in (a,c).
Mentions: 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) However, previous literatures have reported that the Marangoni flow is weak in water droplet329, and our experiments show that deposition is more uniform in CTHC than that on the hot plate (Figs S3 and S4, Mov. S3, S4), which indicates the temperature caused Marangoni flow has weak influence on the deposition morphology. To further reveal the mechanism, we use stereomicroscope to investigate different drying behaviors of droplets with pinned contact line (Mov. S1, S2). When a drop dries at near room temperature (30 °C), obvious outflow induces edge growth process and forms ring-like fashion (Fig. 2a,b). In contrast, a drop drying on heated substrate (70 °C) shows quite inconspicuous growth of the ring region. Interestingly, some angle-dependent iridescence emerges on the surface, which is absence at low temperature (Fig. 2c). This iridescence lasts long until the end of the drying process, and it appears earlier when increasing the substrate temperature. As no pigment was added, we will find that this luster comes from the structure color of ordered assembling of the suspended monodispersed polystyrene particles on drop surface, like color and luster of opal30. This surface assembling process produces increased surface viscosity that is much larger than the bulk4, preventing the suspended particles at air-water interface from moving to the contact line (Fig. 2d).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences (ICCAS), Beijing Engineering Research Center of Nanomaterials for Green Printing Technology, Beijing National Laboratory for Molecular Sciences (BNLMS), Beijing, 100190, P. R. China.

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.

No MeSH data available.