Ji-Won Kim

Bio: Ji-Won Kim is an academic researcher from KAIST. The author has contributed to research in topics: Rock mass classification & Single crystal. The author has an hindex of 7, co-authored 22 publications receiving 107 citations. Previous affiliations of Ji-Won Kim include KAERI.

Smart Microcapsules with Molecular Polarity- and Temperature-Dependent Permeability.

Abstract: Microcapsules with molecule-selective permeation are appealing as microreactors, capsule-type sensors, drug and cell carriers, and artificial cells. To accomplish molecular size- and charge-selective permeation, regular size of pores and surface charges have been formed in the membranes. However, it remains an important challenge to provide advanced regulation of transmembrane transport. Here, smart microcapsules are designed that provide molecular polarity- and temperature-dependent permeability. With capillary microfluidic devices, water-in-oil-in-water (W/O/W) double-emulsion drops are prepared, which serve as templates to produce microcapsules. The oil shell is composed of two monomers and dodecanol, which turns to a polymeric framework whose continuous voids are filled with dodecanol upon photopolymerization. One of the monomers provides mechanical stability of the framework, whereas the other serves as a compatibilizer between growing polymer and dodecanol, preventing macrophase separation. Above melting point of dodecanol, molecules that are soluble in the molten dodecanol are selectively allowed to diffuse across the shell, where the rate of transmembrane transport is strongly influenced by partition coefficient. The rate is drastically lowered for temperatures below the melting point. This molecular polarity- and temperature-dependent permeability renders the microcapsules potentially useful as drug carriers for triggered release and contamination-free microreactors and microsensors.

Controlled Insertion of Planar Defect in Inverse Opals for Anticounterfeiting Applications.

Abstract: Inverse opals have been used for structural coloration and photonic applications owing to their photonic bandgap properties. When the photonic structures contain planar defects, they provide defect modes, which are useful for lasing, sensing, and waveguiding. However, it remains a challenge to insert a planar defect into inverse opals in a reproducible manner. Here, we report a new method for producing planar-defect-inserted inverse opals using sequential capillary wetting of colloidal crystals and creating micropatterns through photolithography. Three cycles of deposition and thermal embedding of colloidal crystals into the underlying film of negative photoresist were performed. In the three cycles, opal, particle monolayer, and opal were sequentially employed, which yielded the monolayer-templated planar defect sandwiched by two inverse opals after particle removal. The planar defect provided a passband whose wavelength can be controlled by adjusting the diameter of particles for the defect layer. Moreo...

Dielectric properties of lithium triborate single crystals

Abstract: From the impedance analysis, we report the dielectric constants of lithium triborate single crystals for the three principal axes in the frequency range of 100 Hz–1 MHz and in the temperature range of 303–773 K. The observed highly anisotropic behavior of dielectric dispersions is mainly related to the anisotropy of the activation energy for Li+ ion hopping, which is constituted by the B3O7 channel framework lain along the c axis.

Local structure of LiB3O5 single crystal from 7Li nuclear magnetic resonance

Abstract: The local structure of LiB3O5 single crystal was investigated with 7Li (I=3/2) nuclear magnetic resonance measurements. We observed four different spectra, which could be divided into two groups corresponding to two kinds of lithium atoms, LiA and LiB, lying at crystallographically equivalent sites and magnetically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature and are e2qQ/h=143±1 kHz and η=0.6±0.1 for 7Li. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have the same principal values of the electric field gradient tensor, but different orientations, and originate from magnetically inequivalent sites. Also, the 7Li spin-lattice relaxation rate was measured, and the measured relaxation rate was found to be proportional to the temperature. The temperature-dependent single phonon process is considered to be more effective than the Raman ...

Deep Ultraviolet Nonlinear Optical Materials

Abstract: Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Multifunctional Chitosan Inverse Opal Particles for Wound Healing

Abstract: Wound healing is one of the most important and basic issues faced by the medical community. In this paper, we present biomass-composited inverse opal particles with a series of advanced features for drug delivery and wound healing. The particles were derived by using chitosan biomass to negatively replicate spherical colloid crystal templates. Because of the interconnected porous structures, various forms of active drugs, including fibroblast growth factor could be loaded into the void spaces of the inverse opal particles and encapsulated by temperature-responsive hydrogel. This endowed the composited particles with the capability of intelligent drug release through the relatively high temperature caused by the inflammation reaction at wound sites. Because the structural colors and characteristic reflection peaks of the composited inverse opal particles are blue-shifted during the release process, the drug delivery can be monitored in real time. It was demonstrated that the biomass-composited microcarrier...

Designing Structural-Color Patterns Composed of Colloidal Arrays.

Abstract: Structural coloration provides a great potential for various applications due to unique optical properties distinguished from conventional pigment colors. Structural colors are nonfading, iridescent, and tunable, which is difficult to achieve with pigments. In addition, structural color is potentially less toxic than pigments. However, it is challenging to develop structural colors because elaborate nanostructures are a prerequisite for the coloration. Furthermore, it is highly suggested the nanostructures be patterned at various length scales on a large area to provide practical formats. There have been intensive studies to develop pragmatic methods for producing structural-color patterns in a controlled manner using either colloidal crystals or glasses. This article reviews the current state of the art in the structural-color patterning based on the colloidal arrays. We first discuss common and different features between colloidal crystals and glasses. We then categorize colloidal arrays into six distinct structures of 3D opals, inverse opals, non-close-packed arrays, 2D colloidal crystals, 1D colloidal strings, and 3D amorphous arrays and study various methods to make them patterned from recent key contributions. Finally, we outline the current challenges and future perspectives of the structural-color patterns.

Dielectric properties of Li2O–3B2O3 glasses

Abstract: The frequency and temperature dependences of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O–3B2O3 were investigated in the 100 Hz–10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were, respectively, analyzed using the Cole–Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole–Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher’s power law. The activation energy associated with the dc conductivity was 0.80±0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O–3B2O3 glasses. These glasses on heating at 933 K/10 h resulted in the known nonlinear optical phase LiB3O5.