Recent Announcement

New paper in Adv. Mater. Interfaces

posted Oct 13, 2017, 6:30 AM by Shin-Hyun Kim

Kwanghwi Je, Ju Hyeon Kim, Tae Soup Shim, Minhee Ku, Jaemoon Yang, and Shin-Hyun Kim, "Lithographically-Designed Conical Microcarriers for Programed Release of Multiple Actives", Advanced Materials InterfacesAccepted for publication (2017).  (Corresponding author)

The programmed release of multiple ingredients is important in the therapeutics and pharmaceutical fields. A variety of core–shell microcarriers have been designed to fulfill the release function; however, encapsulating multiple actives in their own compartments and releasing them in a programmed manner remains a challenge due to restrictions on the material sets that may be used to form the compartments. In this work, we report the development of lithographically featured core–shell microcarriers composed of double cones and a cap that encapsulate and release various combinations of multi-actives in a pre-defined fashion. Active-free caps were first prepared on a photomask using conventional photolithography. Onto each cap were formed, sequentially, an active-loaded small cone and large cone in two steps of reaction diffusion-mediated photolithography (RDP). The release kinetics of the actives stored in the inner and outer cones were controlled by tailoring the cross-linking density of the photocured polymers that composed each compartment. The cap prevented direct diffusion from the inner cone to the surrounding. The RDP-based lithographic means for creating core–shell microcarriers provides new opportunities for delivering synergistic combinations of drugs in pharmacotherapy.

New Article in ACS AM&I

posted Sep 25, 2017, 4:48 PM by Shin-Hyun Kim

Hyelim Kang, Yong Joon Heo, Dong Jae Kim, Ju Hyeon Kim, Tae Yoon Jeon, Soojeong Cho, Hye-Mi So, Won Seok Chang, and Shin-Hyun Kim, "Droplet-Guiding Superhydrophobic Arrays of Plasmonic Microposts for Molecular Concentration and Detection", ACS Applied Materials & Interfaces Accepted for publication (2017).  (Corresponding author) [pdf]

Droplet-guiding superhydrophobic SERS substrates are created by a combinatorial lithographic technique. Photolithography defines the pattern of a micropillar array with a radial density gradient, whereas colloidal lithography features a nanotip array on the top surface of each micropillar. The nanotip array renders the surface superhydrophobic and the pattern of micropillars endows the radial gradient of contact angle, enabling the spontaneous droplet migration toward the center of the pattern. Water droplets containing target molecules are guided to the center and the molecules dissolved in the droplets are concentrated at the surface of the central micropillar during droplet evaporation. Therefore, the molecules can be analyzed at the predefined position by Raman spectra without scanning the entire substrate. At the same time, SERS-active nanotip array provides high sensitivity of Raman measurement.

New Article in ACS Nano

posted Jul 18, 2017, 12:17 AM by Shin-Hyun Kim

Jaeho Choi, Wonhee Cho, Seung Yeol Lee, Yeon Sik Jung, Shin-Hyun Kim, and Hee-Tak Kim, "Flexible and Robust Superomniphobic Surfaces created by Localized Photofluidization of Azopolymer Pillars", ACS Nano Accepted for publication (2017).  (Co-corresponding author)

Springtails, insects which breathe through their skins, possess mushroom-shaped nanostructures. As doubly re-entrant geometry in the mushroom head enhances the resistance against liquid invasion, the springtails have robust, liquid-free omniphobic skins. Although omniphobic surfaces are promising for various applications, it remains an important challenge to mimic the structural feature of springtails. This paper presents a pragmatic method to create doubly re-entrant nanostructures and robust super-omniphobic surfaces by exploiting localized photofluidization of azopolymers. Irradiation of circularly-polarized light reconfigures azopolymer micropillars to have a mushroom-like head with a doubly re-entrant nano-geometry through protrusion and inward bending of polymer film from the top edge. The light-driven reconfigured micropillars facilitate the pining of triple line as the springtails do. In particular, the unique geometry exhibits super-omniphobicity even for liquids whose equilibrium contact angles are almost zero in the presence of a practical level of external pressure. In addition, the simple fabrication process is highly reproducible, scalable, and compatible with various substrate materials including flexible polymeric film. Our results suggest that our photofluidization technology will provide a practical route to develop robust super-omniphobic surfaces.

New Article in Journal of Materials Chemistry C

posted Jul 2, 2017, 4:39 PM by Shin-Hyun Kim

Hyeon Jin Seo, Sang Seok Lee, Jieun Noh, Jae Won Ka, Cheolmin Park, Shin-Hyun Kim, and Yun Ho Kim, "Robust Photonic Microparticles comprised of Cholesteric Liquid Crystals for Anti-forgery Materials", Journal of Materials Chemistry C Accepted for publication (2017)  (Seo & Lee contributed equally, Co-corresponding author)

Cholesteric liquid crystals (CLCs) possess photonic bandgap owing to the helical arrangement of molecules. The CLCs reflect circularly-polarized light of a specific handedness and wavelength, exhibiting colors. The wavelength of the selective reflection, or the structural color, can be easily controlled by varying the concentration of a chiral dopant. Although such a unique optical property renders CLCs promising for various applications, their fluidity severely limits the ease of processing and structural stability. To overcome the limitation, we design CLC microparticles (CLC-MPs) by photopolymerization of reactive mesogens (RMs) in CLC droplets. With capillary microfluidic devices, highly uniform emulsion drops of CLC-RM mixtures are prepared in an aqueous phase drops, which are then exposed to ultraviolet (UV) to yield solid microparticles. The diameter of the CLC-MPs is precisely controlled by either manipulating the flow rates of dispersed and continuous phases or varying the diameter of the capillary orifice in the microfluidic devices. The wavelength of reflection and handedness of helical structure are selected by the composition of the dispersed phase. The photo-polymerization of RMs leads to the formation of a three-dimensional rigid network, thereby yielding the CLC-MPs with high mechanical stability. The CLC-MPs could be further assembled to form two-dimensional hexagonal arrays on flat surfaces or deposited in pre-defined trenches or holes by a mechanical rubbing. Two distinct CLC-MPs with opposite handedness can be patterned to show different color graphics depending on the selection of handedness of circularly-polarized light, which are appealing for anti-forgery patches.

Frontispiece in Advanced Materials

posted Jun 18, 2017, 6:23 AM by Shin-Hyun Kim   [ updated Jun 18, 2017, 6:24 AM ]

Sang Seok Lee, Hyeon Jin Seo,Yun Ho Kim, and Shin-Hyun Kim, "Structural Color Palettes of Core-Shell Photonic Ink Capsules containing Cholesteric Liquid Crystals", Advanced Materials29, 1606894 (2017).(Co-corresponding author

Front Cover Paper in Advanced Materials

posted Jun 11, 2017, 9:21 PM by Shin-Hyun Kim   [ updated Jun 11, 2017, 9:22 PM ]

Soojeong Cho, Tae Soup Shim, Ju Hyeon Kim, Dong-Hyun Kim, and Shin-Hyun Kim, "Selective Coloration of Melanin Nanospheres through Resonant Mie Scattering", Advanced Materials29, 1700256 (2017). [pdf]

New paper in Small

posted May 23, 2017, 9:29 PM by Shin-Hyun Kim

Jing Fan, Shin-Hyun Kim, Zi Chen, Shaobing Zhou, Esther Amstad, Tina Lin, and David A. Weitz, "Creation of faceted polyhedral microgels from compressed emulsions", Small Accepted for publication (2017)  (Fan & Kim contributed equally, Co-corresponding author)

Compressed monodisperse emulsions in confined space exhibit highly ordered structures. We investigate the influence of the volume fraction and the confinement geometry on the organized structures and study the mechanism by which structural transition occurs. Based on the understanding of ordering behavior of compressed emulsions, we develop a simple and high-throughput method to fabricate monodisperse polyhedral microgels using the emulsions as the template. By controlling the geometry of the confined spaces, we implement a variety of shapes such as hexagonal prism, Fejes Toth honeycomb prism, truncated octahedron, pyritohedron, and truncated hexagonal trapezohedron. Moreover, the edge sharpness of each shape is controllable by adjusting the drop volume fraction. This design principle can be readily extended to other shapes and materials, and therefore provides a useful means to create polyhedral microparticles for both fundamental study and practical applications.

New article in ACS AM&I

posted May 3, 2017, 4:44 PM by Shin-Hyun Kim

Sang Seok Lee, Juwoon Park, Yutaek Seo, and Shin-Hyun Kim, "Thermo-Responsive Microcarriers for Smart Release of Hydrate Inhibitors under Shear Flow", ACS Applied Materials & Interfaces Accepted for publication (2017)

New paper in Small

posted Apr 18, 2017, 7:42 PM by Shin-Hyun Kim

Tae Yong Lee, Minhee Ku, Bomi Kim, Sangmin Lee, Jaemoon Yang and Shin-Hyun Kim, "Microfluidic Production of Biodegradable Microcapsules for Sustained Release of Hydrophilic Actives", Small Accepted for publication (2017)  (Corresponding author

New Paper in Small

posted Mar 8, 2017, 8:40 PM by Shin-Hyun Kim

Dong Jae Kim, Tae Yoon Jeon, Sung-Gyu Park, Hye Ji Han, Sang Hyuk Im, Dong-Ho Kim and Shin-Hyun Kim, "Uniform Microgels containing Agglomerates of Silver Nanocubes for Molecular Size-Selectivity and High SERS Activity", Small, accepted for publication (2017).

Microgels containing agglomerates of silver nanocubes are microfluidically created to provide SERS-active substrates. The microgels permit selective infusion of small molecules and nanogaps among the nanocubes serve as hot spots for SERS. Therefore, the microgels enable us to selectively analyze Raman spectra of small molecules dissolved in complex mixtures with high sensitivity in the absence of interruption from large adhesives.

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