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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.


Race between interface descending rate and the corresponding average particle diffusion rate determines the dominance of edge accumulation or surface accumulation.(a) Schematic of the rate-dependent interface capture process. (b) Drop apex descending evolution at different evaporation temperature. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times. (c) Phase diagram of the deposition morphology at different evaporation rate. Rapid growth of average interface descending rate vi and the corresponding particle average diffusion rate xp declares the dominant field of coffee-ring effect (blue) at low evaporation temperature and surface accumulation (red) at high temperature, green region represent the transition zone of these two process.
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f4: Race between interface descending rate and the corresponding average particle diffusion rate determines the dominance of edge accumulation or surface accumulation.(a) Schematic of the rate-dependent interface capture process. (b) Drop apex descending evolution at different evaporation temperature. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times. (c) Phase diagram of the deposition morphology at different evaporation rate. Rapid growth of average interface descending rate vi and the corresponding particle average diffusion rate xp declares the dominant field of coffee-ring effect (blue) at low evaporation temperature and surface accumulation (red) at high temperature, green region represent the transition zone of these two process.

Mentions: Real-time evaporation kinetics records validate this rate-dependent interface capture process. We use video microscopy to quantify the spatio-temporal evaporation profile of the droplet drying at different temperature (inset in Movie S1, S2, and Fig. S6). The race between interface receding and particle diffusion reverses by the acceleration of evaporation, which determines the main direction of particle flow during the drying process (Fig. 4). At low evaporation rate, particles diffuse faster than the descending interface that the air-liquid interface fails to capture these nimble particles. Therefore, they still disperse evenly in the entire drop and finally transport to the contact line by capillary outflow. However, this unbalance situation could be changed by controlling evaporation rate. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times (Fig. 4b). According to calculation, the average interface descending rate vi = h/tf grows faster than the particle average diffusion rate xp = 2(Dt/π)1/2 (per second) when rising the evaporation temperature. Here h is the original height of droplet, tf the final evaporation time; the diffusion constant D is estimated from the Stokes-Einstein relation D = kBT/6πηr, where kB is Boltzmann’s constant, T the temperature, η the viscosity of solvent, and r the hydrodynamic radius of the particles which approximates to spherical particle radius. When the surface descends faster than the particle diffusion, particles of random walk in vertical evaporation flow will be captured by the drop surface (Fig. 4a), as shown in the simulation process (S7, Mov. S5). In this drop system, the changeover is realized near 40 °C and the interface velocity is large enough to capture the logy particles near surface. When impinge the air-liquid interface, these captured particles will assemble into isolated islands by lateral capillary force39. Particle islands appear and then piece together to form continuous layer with continuous evaporation, which consists well with the observation results in Fig. 3. Further temperature rising will accelerate the islands growth, incorporation and thickness growth of solid layer.


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

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

Race between interface descending rate and the corresponding average particle diffusion rate determines the dominance of edge accumulation or surface accumulation.(a) Schematic of the rate-dependent interface capture process. (b) Drop apex descending evolution at different evaporation temperature. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times. (c) Phase diagram of the deposition morphology at different evaporation rate. Rapid growth of average interface descending rate vi and the corresponding particle average diffusion rate xp declares the dominant field of coffee-ring effect (blue) at low evaporation temperature and surface accumulation (red) at high temperature, green region represent the transition zone of these two process.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Race between interface descending rate and the corresponding average particle diffusion rate determines the dominance of edge accumulation or surface accumulation.(a) Schematic of the rate-dependent interface capture process. (b) Drop apex descending evolution at different evaporation temperature. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times. (c) Phase diagram of the deposition morphology at different evaporation rate. Rapid growth of average interface descending rate vi and the corresponding particle average diffusion rate xp declares the dominant field of coffee-ring effect (blue) at low evaporation temperature and surface accumulation (red) at high temperature, green region represent the transition zone of these two process.
Mentions: Real-time evaporation kinetics records validate this rate-dependent interface capture process. We use video microscopy to quantify the spatio-temporal evaporation profile of the droplet drying at different temperature (inset in Movie S1, S2, and Fig. S6). The race between interface receding and particle diffusion reverses by the acceleration of evaporation, which determines the main direction of particle flow during the drying process (Fig. 4). At low evaporation rate, particles diffuse faster than the descending interface that the air-liquid interface fails to capture these nimble particles. Therefore, they still disperse evenly in the entire drop and finally transport to the contact line by capillary outflow. However, this unbalance situation could be changed by controlling evaporation rate. Increasing evaporation temperature accelerates the surface descending rate and decreases the average drying times (Fig. 4b). According to calculation, the average interface descending rate vi = h/tf grows faster than the particle average diffusion rate xp = 2(Dt/π)1/2 (per second) when rising the evaporation temperature. Here h is the original height of droplet, tf the final evaporation time; the diffusion constant D is estimated from the Stokes-Einstein relation D = kBT/6πηr, where kB is Boltzmann’s constant, T the temperature, η the viscosity of solvent, and r the hydrodynamic radius of the particles which approximates to spherical particle radius. When the surface descends faster than the particle diffusion, particles of random walk in vertical evaporation flow will be captured by the drop surface (Fig. 4a), as shown in the simulation process (S7, Mov. S5). In this drop system, the changeover is realized near 40 °C and the interface velocity is large enough to capture the logy particles near surface. When impinge the air-liquid interface, these captured particles will assemble into isolated islands by lateral capillary force39. Particle islands appear and then piece together to form continuous layer with continuous evaporation, which consists well with the observation results in Fig. 3. Further temperature rising will accelerate the islands growth, incorporation and thickness growth of solid layer.

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.