Drying, Coating, & Printing
We study how colloids pack each other and leave a specific pattern, which can be changed by the surface condition of colloids and working fluid. We focus on optimizing the coating solution system to obtain a uniform pattern. Additionally, we endeavor to develop a novel control coating method, in particular ordered versus disordered packing structures. Our coating method can be applied to the organic or inorganic materials coating or printing technologies. Furthermore, to combine our developed model and 2D or 3D printing technologies, we will construct a printing system for mass production manufacturing.
Cellulose nanocrystals (CNCs) are intriguing as a matrix for plasmonic meta-surfaces made of gold nanorods (GNRs) because of their distinctive properties, including renewability, biodegradability, non-toxicity, and low cost. Nevertheless, it is very difficult to precisely regulate the positioning and orientation of CNCs on the substrate in a consistent pattern. In this study, CNCs and GNRs, which exhibit tunable optical and anti-icing capabilities, are employed to manufacture a uniform plasmonic metasurface using a drop-casting technique. Two physical phenomena—(i) spontaneous and rapid self-dewetting and (ii) evaporation-induced self-assembly—are used to accomplish this. Additionally, we improve the CNC-GNR ink composition and determine the crucial coating parameters necessary to balance the two physical mechanisms to produce thin films without coffee rings. The final homogeneous CNC- GNR film has consistent annular ring patterns with plasmonic quadrant hues that are properly aligned, which enhances plasmonic photothermal effects. The CNC-GNR multi-array platform offers above-zero temperatures on a substrate that is subcooled below the freezing point. The current study presents a physicochemical approach for functional nanomaterial-based CNC control.
Related publication: J. Pyeon, S. Park, J. Kim, J.-H. Kim, Y.-J. Yoon, D.-K. Yoon, H. Kim, "Homogeneous quadrant cellulose nanocrystal matrices by fast evaporative dewetting change plasmonic effect of co-assembled gold nanorods," Nat. Commun. 14:8096
Controlled exps
Not controlled exps
In this study, we present a novel idea to control the nucleation location of surfactant crystallization by using vapor-driven solutal Marangoni effects of a binary mixture drop in a confined chamber. Here, the evaporated volatile vapors near the droplet surface can change the local surface tension and generate a radially inward flow that suppresses the conventional coffee-ring flow (i.e., evaporatively-driven capillary flow). Using this method, we could accumulate suspended particles in the middle of the droplet. In consequence, we succeed in adjusting the nucleation location from the droplet edge to the center provided that a gel-transition process is neglected, where the crystallized material has a relatively long chain length. We expect that the proposed idea can offer great potential for controlling the nucleation in the evaporative crystallization and its final crystalline solid morphology.
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Related publication: J. Pyeon, S. M. Park, D. K. Yoon, H. Kim, "Controlled nucleation in evaporative crystallization using confined-vapor driven solutal Marangoni effect," accepted in Soft Matter (Cover).
A coffee-ring stain is still a bottleneck, which is extremely crucial in coating industry related to printed electronics and nanotechnology. Due to this reason, the unresolved and problematic issue has received a great attention in various research areas. In this work, we show a novel and economical method of coffee-ring-less quantum dot microarrays for the better performance of the QD display. The current method is allowed to fabricate various polygonal shapes of QD patterns and it is easy to scale down and/or up using a surface condition and an isolation chamber. Based on the flow field measurement technique, we showed that the polygonal shape droplet of the binary mixture solution can control the internal solutal Marangoni flows using geometric factors of the droplet. Evaporatively self-induced sequential Marangoni flows yielded a coffee-ring-less QD microarrays. In the current work, we used the most famous binary solution (ethanol-water mixture) but it is known as that it is extremely hard to control the flow structures due to nonlinear features. However, we successfully controlled the flow pattern and finally achieved coffee-ring-less dried pattern. We can also extend this idea to any mixture, if two liquids have a different vapor pressure and surface tension value where the volatile liquid should have a heavier molecular weight compared to the ambient gas. We believe that our method is relevant to many research areas that utilize coating technologies, complex fluids and physicochemical hydrodynamics, e.g., engineering, applied physics, fluid dynamics, chemical physics, and material science.
Related publication: J. Pyeon, K. M. Song, Y. Jung, and H. Kim, "Self-induced solutal Marangoni flows realize coffee-ring-less quantum dot microarrays with extensive geometric tunability and scalability," Adv. Sci. 2104519 (2022)
DNA is a common biomaterial in nature as well as a good building block for producing useful structures, due to its fine feature size and liquid crystalline phase. Here, we demonstrate that a combination of shear-induced flow and microposts can be used to create various kinds of interesting microstructure DNA arrays. Our facile method provides a platform for forming multi-scale hierarchical orientations of soft- and biomaterials, using a process of simple shearing and controlled evaporation on a patterned substrate. This approach enables potential patterning applications using DNA or other anisotropic biomaterials based on their unique structural characteristics.
Related publication: Cha YJ; Park SM; Kim H; and Yoon DK, "Microstructure arrays of DNA using topographic control," NATURE COMMUNICATIONS
Colloidal crystals exhibit structural color without any color pigment due to the crystals’ periodic nanostructure, which can interfere with visible light. This crystal structure is iridescent as the resulting color changes with the viewing or illumination angle, which limits its use for printing or displays. To eliminate the iridescent property, it is important to make the packing of the colloidal nanoparticles disordered. Here, we introduce a drop-casting method where a droplet of a water- ethanol mixture containing monodisperse polymer-coated silica nanoparticles creates a relatively uniform and non-iridescent deposit after the droplet evaporates completely on a heated substrate. The uniformity is caused by a thermal Marangoni flow and fast evaporation effects due to the heated substrate, whereas non-iridescence is the outcome of short-range-ordered packing of nanoparticles by depletion attraction and friction effects produced by polymer brushes. We show that the colors of the final deposits from individual droplets remain unchanged while the viewing angle is varied under ambient light. We expect that the coating method is compatible with ink-jet printing and the uniformly coated self-assembled non-iridescent nanostructures have potential for color displays using reflection mode and other optical devices.
Related publication:
S. Y. Lee, H. Kim, S.-H. Kim, and H.A. Stone "Uniform coating of self-assembled noniridescent colloidal nanostructures using the Marangoni effect and polymers," PHYSICAL REVIEW APPLIED, accepted. [PDF] (Impact factor: 4.782)
A single monolayer coating of colloidal particles is extensively studied over last several decades. However, to stack multiple layers of particles with a uniform thickness is still lacking and the fabrication process can be typically complex. Here, we study how condensed colloidal particles uniformly coat on a substance with a single-step coating method. We expect this coating method can be used for ink-jet printing and 3D-printing technologies. We are also interested in manipulating packing shape of the colloidal structure using physico-chemical effects. The detail research results would be described in the near future.
<Cross-section>
<Top view>
Ellipsoidal particles have previously been shown to suppress the coffee-ring effect in millimeter-sized colloidal droplets. Compared to their spherical counterparts, ellipsoidal particles experience stronger adsorption energy to the drop surface where the anisotropy-induced deformation of the liquid−air interface leads to much greater capillary attractions between particles. Using inkjet-printed colloidal drops of varying drop size, particle concentration, and particle aspect ratio, the present work demonstrates how the suppression of the coffee ring is not only a function of particle anisotropy but rather a competition between the propensity for particles to assemble at the drop surface via capillary interactions and the evaporation-driven particle motion to the contact line. For ellipsoidal particles on the drop surface, the capillary force (Fγ) increases with the particle concentration and aspect ratio, and the hydrodynamic force (Fμ) increases with the particle aspect ratio but decreases with drop size. When Fγ/Fμ > 1, the surface ellipsoids form a coherent network inhibiting their migration to the drop contact line, and the coffee-ring effect is suppressed, whereas when Fγ/Fμ < 1, the ellipsoids move to the contact line, resulting in coffee-ring deposition.
Related publication:
D.-O. Kim, M. Pack, H. Hu, H. Kim, and Y. Sun, “Deposition of Colloidal Drops Containing Ellipsoidal Particles: Competition between Capillary and Hydrodynamic Forces,” Langmuir 32(45), 11899 (2016)
Controlled exps
Not controlled exps
In this study, we present a novel idea to control the nucleation location of surfactant crystallization by using vapor-driven solutal Marangoni effects of a binary mixture drop in a confined chamber. Here, the evaporated volatile vapors near the droplet surface can change the local surface tension and generate a radially inward flow that suppresses the conventional coffee-ring flow (i.e., evaporatively-driven capillary flow). Using this method, we could accumulate suspended particles in the middle of the droplet. In consequence, we succeed in adjusting the nucleation location from the droplet edge to the center provided that a gel-transition process is neglected, where the crystallized material has a relatively long chain length. We expect that the proposed idea can offer great potential for controlling the nucleation in the evaporative crystallization and its final crystalline solid morphology.
​
Related publication: J. Pyeon, S. M. Park, D. K. Yoon, H. Kim, "Controlled nucleation in evaporative crystallization using confined-vapor driven solutal Marangoni effect," accepted in Soft Matter (Cover).
A coffee-ring stain is still a bottleneck, which is extremely crucial in coating industry related to printed electronics and nanotechnology. Due to this reason, the unresolved and problematic issue has received a great attention in various research areas. In this work, we show a novel and economical method of coffee-ring-less quantum dot microarrays for the better performance of the QD display. The current method is allowed to fabricate various polygonal shapes of QD patterns and it is easy to scale down and/or up using a surface condition and an isolation chamber. Based on the flow field measurement technique, we showed that the polygonal shape droplet of the binary mixture solution can control the internal solutal Marangoni flows using geometric factors of the droplet. Evaporatively self-induced sequential Marangoni flows yielded a coffee-ring-less QD microarrays. In the current work, we used the most famous binary solution (ethanol-water mixture) but it is known as that it is extremely hard to control the flow structures due to nonlinear features. However, we successfully controlled the flow pattern and finally achieved coffee-ring-less dried pattern. We can also extend this idea to any mixture, if two liquids have a different vapor pressure and surface tension value where the volatile liquid should have a heavier molecular weight compared to the ambient gas. We believe that our method is relevant to many research areas that utilize coating technologies, complex fluids and physicochemical hydrodynamics, e.g., engineering, applied physics, fluid dynamics, chemical physics, and material science.
Related publication: J. Pyeon, K. M. Song, Y. Jung, and H. Kim, "Self-induced solutal Marangoni flows realize coffee-ring-less quantum dot microarrays with extensive geometric tunability and scalability," Adv. Sci. 2104519 (2022)
DNA is a common biomaterial in nature as well as a good building block for producing useful structures, due to its fine feature size and liquid crystalline phase. Here, we demonstrate that a combination of shear-induced flow and microposts can be used to create various kinds of interesting microstructure DNA arrays. Our facile method provides a platform for forming multi-scale hierarchical orientations of soft- and biomaterials, using a process of simple shearing and controlled evaporation on a patterned substrate. This approach enables potential patterning applications using DNA or other anisotropic biomaterials based on their unique structural characteristics.
Related publication: Cha YJ; Park SM; Kim H; and Yoon DK, "Microstructure arrays of DNA using topographic control," NATURE COMMUNICATIONS
Colloidal crystals exhibit structural color without any color pigment due to the crystals’ periodic nanostructure, which can interfere with visible light. This crystal structure is iridescent as the resulting color changes with the viewing or illumination angle, which limits its use for printing or displays. To eliminate the iridescent property, it is important to make the packing of the colloidal nanoparticles disordered. Here, we introduce a drop-casting method where a droplet of a water- ethanol mixture containing monodisperse polymer-coated silica nanoparticles creates a relatively uniform and non-iridescent deposit after the droplet evaporates completely on a heated substrate. The uniformity is caused by a thermal Marangoni flow and fast evaporation effects due to the heated substrate, whereas non-iridescence is the outcome of short-range-ordered packing of nanoparticles by depletion attraction and friction effects produced by polymer brushes. We show that the colors of the final deposits from individual droplets remain unchanged while the viewing angle is varied under ambient light. We expect that the coating method is compatible with ink-jet printing and the uniformly coated self-assembled non-iridescent nanostructures have potential for color displays using reflection mode and other optical devices.
Related publication:
S. Y. Lee, H. Kim, S.-H. Kim, and H.A. Stone "Uniform coating of self-assembled noniridescent colloidal nanostructures using the Marangoni effect and polymers," PHYSICAL REVIEW APPLIED, accepted. [PDF] (Impact factor: 4.782)
A single monolayer coating of colloidal particles is extensively studied over last several decades. However, to stack multiple layers of particles with a uniform thickness is still lacking and the fabrication process can be typically complex. Here, we study how condensed colloidal particles uniformly coat on a substance with a single-step coating method. We expect this coating method can be used for ink-jet printing and 3D-printing technologies. We are also interested in manipulating packing shape of the colloidal structure using physico-chemical effects. The detail research results would be described in the near future.
<Cross-section>
<Top view>
Ellipsoidal particles have previously been shown to suppress the coffee-ring effect in millimeter-sized colloidal droplets. Compared to their spherical counterparts, ellipsoidal particles experience stronger adsorption energy to the drop surface where the anisotropy-induced deformation of the liquid−air interface leads to much greater capillary attractions between particles. Using inkjet-printed colloidal drops of varying drop size, particle concentration, and particle aspect ratio, the present work demonstrates how the suppression of the coffee ring is not only a function of particle anisotropy but rather a competition between the propensity for particles to assemble at the drop surface via capillary interactions and the evaporation-driven particle motion to the contact line. For ellipsoidal particles on the drop surface, the capillary force (Fγ) increases with the particle concentration and aspect ratio, and the hydrodynamic force (Fμ) increases with the particle aspect ratio but decreases with drop size. When Fγ/Fμ > 1, the surface ellipsoids form a coherent network inhibiting their migration to the drop contact line, and the coffee-ring effect is suppressed, whereas when Fγ/Fμ < 1, the ellipsoids move to the contact line, resulting in coffee-ring deposition.
Related publication:
D.-O. Kim, M. Pack, H. Hu, H. Kim, and Y. Sun, “Deposition of Colloidal Drops Containing Ellipsoidal Particles: Competition between Capillary and Hydrodynamic Forces,” Langmuir 32(45), 11899 (2016)