Jongwon Shim - Academia.edu (original) (raw)

Papers by Jongwon Shim

Research paper thumbnail of Two-or three-dimensional interfacial self-assembly of graphene platelets = 그래핀의 2차원 또는 3차원 계면 자기 조립

Research paper thumbnail of Preparation and Characterization of Cerium Oxide/Silica Composite Particles

Applied Chemistry for Engineering, 2018

Composite particles of porous silica and cerium oxide nanoparticles blocking UV/blue light were p... more Composite particles of porous silica and cerium oxide nanoparticles blocking UV/blue light were prepared through a dry coating process. Various composite particles were prepared by varying conditions such as the mixing ratio of cerium oxide and silica, and the chamber rotating speed of mechano fusion system. The surface morphology of the composite particles was observed with SEM and the composition was analyzed using X-ray fluorescence (XRF). When the cerium oxide/silica composite particles were dispersed in water, the transparency and dispersion stability of the colloidal solution were improved. In addition, the fluidity and spreadability of the particle powder were enhanced by making composite particles. These results show that cerium oxide/silica composite particles can be used as functional cosmetic ingredients for UV/blue light protection.

Research paper thumbnail of Graphene: Microtopography-Guided Conductive Patterns of Liquid-Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array (Adv. Mater. 21/2017)

Advanced Materials, Jun 1, 2017

Graphene nanoplates can be assembled into transparent and conductive ultrathin coatings on microp... more Graphene nanoplates can be assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates by self-assembly via a convective Marangoni force. Based on this method, Sang Ouk Kim, Changhyun Pang, and co-workers fabricate a thin, stretchable, and skin-conformal strain-sensor array that has microtopography-guided, conductive patterns.

Research paper thumbnail of Inhibition of Melanin Synthesis by Enhanced Cytosolic Delivery of N-glycosylation Inhibitors Using pH-Sensitive Nano-carrier

Journal of the Society of Cosmetic Scientists of Korea, 2004

Research paper thumbnail of Non-invasive Transdermal Delivery Route Using Electrostatically Interactive Biocompatible Nanocapsules

Advanced Materials, Feb 9, 2010

Research paper thumbnail of Microtopography-Guided Conductive Patterns of Liquid-Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array

Advanced Materials, Mar 29, 2017

Wearable and implantable devices aiming at biomedical diagnosis or therapy have been developed by... more Wearable and implantable devices aiming at biomedical diagnosis or therapy have been developed by integrating multiple functions, [1,2] such as high bendability or stretchability, [3,4] transparency, [5,6] conformal contacts on biosurfaces, [7,8] and low Flexible thin-film sensors have been developed for practical uses in invasive or noninvasive cost-effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ-conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin-conformal sensor array (144 pixels) is fabricated having microtopography-guided, graphene-based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin-like stretchability (<48%), high cyclic stability or durability (over 10 5 cycles), and the signal amplification (≈5.25 times) via structureassisted intimate-contacts between the device and rough skin. Furthermore, given the thin-film programmable architecture and mechanical deformability of the sensor, a human skin-conformal sensor is demonstrated with a wireless transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse-waveforms and evolved into a mechanical/thermal-sensitive electric rubber-balloon and an electronic blood-vessel. The microtopography-guided and self-assembled conductive patterns offer highly promising methodology and tool for next-generation biomedical devices and various flexible/stretchable (wearable) devices.

Research paper thumbnail of Liquid Crystal Size Selection of Large-Size Graphene Oxide for Size-Dependent N-Doping and Oxygen Reduction Catalysis

ACS Nano, Sep 2, 2014

Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic li... more Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic liquid crystallinity. Many properties of GO-based materials, including electrical conductivity and mechanical properties, are limited by the small flake size of GO. Unfortunately, typical sonochemical exfoliation of GO from graphite generally leads to a broad size and shape distribution. Here, we introduce a facile size selection of large-size GO exploiting liquid crystallinity and investigate the size-dependent N-doping and oxygen reduction catalysis. In the biphasic GO dispersion where both isotropic and liquid crystalline phases are equilibrated, large-size GO flakes (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;20 μm) are spontaneously concentrated within the liquid crystalline phase. N-Doping and reduction of the size-selected GO exhibit that N-dopant type is highly dependent on GO flake size. Large-size GO demonstrates quaternary dominant N-doping and the lowest onset potential (-0.08 V) for oxygen reduction catalysis, signifying that quaternary N-dopants serve as principal catalytic sites in N-doped graphene.

Research paper thumbnail of Flexible Magnetic Microtubules Structured by Lipids and Magnetic Nanoparticles

ACS Applied Materials & Interfaces, May 11, 2009

This study presents a microtubule that responds to a magnetic field. We made such a structure by ... more This study presents a microtubule that responds to a magnetic field. We made such a structure by incorporating iron oxide nanoparticles during the preparation of the microtubule. We found that the microtubule stretches its body when the magnetic field is applied and easily aligns with the direction of the applied magnetic field by rotating its body. When the magnetic field is removed, it loses its orientation and goes back to its original state by contraction. From the analysis of its magnetic response, we estimated that the magnetic microtubule had an elastic modulus of 33 MPa. Further analysis showed that the stretching and contracting of its body are due to its flexibility.

Research paper thumbnail of Improved stability of liposome in oil/water emulsion by association of amphiphilic polymer with liposome and its effect on bioactive skin permeation

Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2007

In this study, we demonstrated that the stability of phosphatidylcholine (PC)-cholesterol (Chol) ... more In this study, we demonstrated that the stability of phosphatidylcholine (PC)-cholesterol (Chol) liposomes can be improved in oil in water (o/w) emulsion by association of amphiphilic polyelectrolyte, poly(methacrylic acid-co-stearyl methacrylate) with PC–Chol liposomes. Differential scanning calorimetry and photocorrelation spectroscopy results showed that the polymer-associated liposomes were more stable than the PC–Chol liposomes when mixed with the o/w emulsion. This difference

Research paper thumbnail of Effect of a Surfactant in Microcapsule Synthesis on Self-Healing Behavior of Capsule Embedded Polymeric Films

Polymers, Jun 17, 2018

Recently, there has been increased interest in self-healing membranes containing functional micro... more Recently, there has been increased interest in self-healing membranes containing functional microcapsules in relation to challenges involving water treatment membranes. In this study, a self-healing membrane has been prepared by incorporating microcapsules with a polyurethane (PU) shell and a diisocyanate core in a poly(ether sulfone) (PES) membrane. Depending on the characteristics of the microcapsule, to precisely quantify the self-healing behavior and performance of the produced microcapsule embedded membranes, it is important to understand the effect of a used surfactant on microcapsule synthesis. It is noteworthy that mixed surfactants have been employed to control and tailor the size and morphology of microcapsules during the synthetic process, and the surfactant system employed was one of the most dominant parameters for affecting the healing capability of microcapsule embedded membranes. Various techniques including microscopy (optical and electron), thermal analyses (DSC and TGA), and water flux measurements have been employed. This article provides essential and important information for future research into the subtle relation between microcapsule properties with varied synthetic parameters and the self-healing behavior of membrane.

Research paper thumbnail of Carbon: 25th Anniversary Article: Chemically Modified/Doped Carbon Nanotubes & Graphene for Optimized Nanostructures & Nanodevices (Adv. Mater. 1/2014)

Research paper thumbnail of One-pot microfluidic fabrication of graphene oxide-patched hollow hydrogel microcapsules with remarkable shell impermeability

Chemical Communications, 2015

Research paper thumbnail of Ultrafast Interfacial Self-Assembly of 2D Transition Metal Dichalcogenides Monolayer Films and Their Vertical and In-Plane Heterostructures

ACS Applied Materials & Interfaces, Dec 28, 2016

Cost effective scalable method for uniform film formation is highly demanded for the emerging app... more Cost effective scalable method for uniform film formation is highly demanded for the emerging applications of 2D transition metal dichalcogenides (TMDs). We demonstrate a reliable and fast interfacial self-assembly of TMD thin films and their heterostructures. Large-area 2D TMD monolayer films are assembled at air-water interface in a few minutes by simple addition of ethyl acetate (EA) onto dilute aqueous dispersions of TMDs. Assembled TMD films can be directly transferred onto arbitrary nonplanar and flexible substrates. Precise thickness controllability of TMD thin films, which is essential for thickness-dependent applications, can be readily obtained by the number of film stacking. Most importantly, complex structures such as laterally assembled 2D heterostructures of TMDs can be assembled from mixture solution dispersions of two or more different TMDs. This unusually fast interfacial self-assembly could open up a novel applications of 2D TMD materials with precise tunability of layer number and film structures.

Research paper thumbnail of Nanosized Emulsions Stabilized by Semisolid Polymer Interphase

Langmuir, Aug 17, 2010

We introduce a new approach for stabilizing oil-in-water nanoemulsions using a semisolid interpha... more We introduce a new approach for stabilizing oil-in-water nanoemulsions using a semisolid interphase formed by the phase separation of amphiphilic block copolymers from the organic phase. This system is illustrated using an amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL), with commonly used oils. PEO-b-PCL can be miscible with oil at elevated temperatures (70-80°C); however, polymer/oil demixing occurs as the temperature drops below the melting temperature of PEO-b-PCL (∼55°C). A homogeneous polymer/oil mixture was dispersed in water at 80°C to generate embryonic emulsions, and then the emulsion size was reduced to a nanometer range through microfluidic homogenization. The structure of the generated nanoemulsions is irreversibly frozen as they are cooled down to ambient temperature. The nanoemulsions stabilized by PEO-b-PCL show the excellent colloidal stability against thermal and chemical stresses, exhibiting no significant changes in the size distribution during incubation for 4 months at ambient temperature or 10 days at 60°C. This study demonstrates that PEO-b-PCL is an attractive emulsifying material for practical nanoemulsion formulations requiring structural stability under a broad range of conditions.

Research paper thumbnail of Silicone oil emulsions stabilized by semi-solid nanostructures entrapped at the interface

Journal of Colloid and Interface Science, Nov 1, 2010

Oil-in-water (O/W) emulsions are typically stabilized using water-soluble surfactants, which anch... more Oil-in-water (O/W) emulsions are typically stabilized using water-soluble surfactants, which anchor to the surface of oil droplets dispersed in an aqueous solution. The structure of the anchored surfactants is often susceptible to physical and chemical stresses because of their highly mobile properties. Here we introduce a new approach to prepare stable silicone oil emulsions under various external stresses using a water-insoluble amphiphilic block copolymer, poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL). Above the melting temperature (around 60 degrees C) of the hydrophobic segment (PCL), PEO-b-PCL can be dissolved in silicone oil. When the polymer/oil mixture is dispersed in water, PEO-b-PCL is irreversibly reorganized into solid nanostructures at the interface of the aqueous/organic phases. The resulting interfacial structures provide a robust physical barrier to the emulsion coarsening processes. Accordingly, the prepared emulsions exhibit excellent structural tolerance against external stresses, including variations in pH, ionic strength, and temperature.

Research paper thumbnail of A Simple Evaporation Method for Large-Scale Production of Liquid Crystalline Lipid Nanoparticles with Various Internal Structures

ACS Applied Materials & Interfaces, Aug 25, 2015

Research paper thumbnail of Transdermal delivery of mixnoxidil with block copolymer nanoparticles

Journal of Controlled Release, Jul 7, 2004

We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration ... more We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration of minoxidil in vitro and in vivo. Self-assembled 40-and 130-nm nanoparticles, both containing minoxidil, were prepared by solvent evaporation of poly(q-caprolactone)-block-poly(ethyleneglycol) and were applied onto the skin of both hairy and hairless guinea pigs in the Franz diffusion cell. In hairy guinea pig skin, the permeation of the minoxidil that incorporated in 40-nm nanoparticles was 1.5fold higher in the epidermal layer and 1.7-fold higher in the receptor solution than that of 130-nm nanoparticles. Nanoparticle size dependence on the permeation behavior of minoxidil was not observed for hairless guinea pig skin in either the epidermal layer or the receptor solution. Phospholipid liposomes and ethanol-water admixture, on the other hand, containing the same amount of minoxidil did not show differences in the amount of permeation irrespective of the existence of hair follicles. Confocal microscopy coupled with in vivo and in vitro skin permeation results demonstrated that nanoparticles containing solutes penetrated mainly via shunt routes like hair follicles, resulting in skin absorption of solutes.

Research paper thumbnail of The skin-permeation-enhancing effect of phosphatidylcholine: caffeine as a model active ingredient

PubMed, Jan 4, 2003

Phospholipids or liposomes are recognized to have skin permeation enhancing ability, although the... more Phospholipids or liposomes are recognized to have skin permeation enhancing ability, although their mechanisms are still controversial. The aim of this study was to establish a method of increasing the skin permeation of active ingredients, using phosphatidylcholine as a permeation enhancer. Caffeine was used as a model active ingredient and in vitro skin penetration experiments were performed using Franz-type diffusion cells to determine the amount of absorbed caffeine. Lipid vesicles were prepared by the microfluidization process. The encapsulation efficiency of caffeine was found to be very low due to the instability of the liposome structure and the water solubility of caffeine. However, the amount of absorbed caffeine was nearly independent of the encapsulation efficiency and the vesicle size, but increased with the increase of phosphatidylcholine concentration. These results indicated that phosphatidylcholine could act as a penetration enhancer, irrespective of its presence in vesicular form or solubilized form.

Research paper thumbnail of Case study on stability analysis of large rock slopes by stereophotogrammetry in highway construction project

Research paper thumbnail of 25th Anniversary Article: Chemically Modified/Doped Carbon Nanotubes & Graphene for Optimized Nanostructures & Nanodevices

Advanced Materials, Oct 14, 2013

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real‐... more Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real‐life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.

Research paper thumbnail of Two-or three-dimensional interfacial self-assembly of graphene platelets = 그래핀의 2차원 또는 3차원 계면 자기 조립

Research paper thumbnail of Preparation and Characterization of Cerium Oxide/Silica Composite Particles

Applied Chemistry for Engineering, 2018

Composite particles of porous silica and cerium oxide nanoparticles blocking UV/blue light were p... more Composite particles of porous silica and cerium oxide nanoparticles blocking UV/blue light were prepared through a dry coating process. Various composite particles were prepared by varying conditions such as the mixing ratio of cerium oxide and silica, and the chamber rotating speed of mechano fusion system. The surface morphology of the composite particles was observed with SEM and the composition was analyzed using X-ray fluorescence (XRF). When the cerium oxide/silica composite particles were dispersed in water, the transparency and dispersion stability of the colloidal solution were improved. In addition, the fluidity and spreadability of the particle powder were enhanced by making composite particles. These results show that cerium oxide/silica composite particles can be used as functional cosmetic ingredients for UV/blue light protection.

Research paper thumbnail of Graphene: Microtopography-Guided Conductive Patterns of Liquid-Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array (Adv. Mater. 21/2017)

Advanced Materials, Jun 1, 2017

Graphene nanoplates can be assembled into transparent and conductive ultrathin coatings on microp... more Graphene nanoplates can be assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates by self-assembly via a convective Marangoni force. Based on this method, Sang Ouk Kim, Changhyun Pang, and co-workers fabricate a thin, stretchable, and skin-conformal strain-sensor array that has microtopography-guided, conductive patterns.

Research paper thumbnail of Inhibition of Melanin Synthesis by Enhanced Cytosolic Delivery of N-glycosylation Inhibitors Using pH-Sensitive Nano-carrier

Journal of the Society of Cosmetic Scientists of Korea, 2004

Research paper thumbnail of Non-invasive Transdermal Delivery Route Using Electrostatically Interactive Biocompatible Nanocapsules

Advanced Materials, Feb 9, 2010

Research paper thumbnail of Microtopography-Guided Conductive Patterns of Liquid-Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array

Advanced Materials, Mar 29, 2017

Wearable and implantable devices aiming at biomedical diagnosis or therapy have been developed by... more Wearable and implantable devices aiming at biomedical diagnosis or therapy have been developed by integrating multiple functions, [1,2] such as high bendability or stretchability, [3,4] transparency, [5,6] conformal contacts on biosurfaces, [7,8] and low Flexible thin-film sensors have been developed for practical uses in invasive or noninvasive cost-effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ-conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin-conformal sensor array (144 pixels) is fabricated having microtopography-guided, graphene-based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin-like stretchability (<48%), high cyclic stability or durability (over 10 5 cycles), and the signal amplification (≈5.25 times) via structureassisted intimate-contacts between the device and rough skin. Furthermore, given the thin-film programmable architecture and mechanical deformability of the sensor, a human skin-conformal sensor is demonstrated with a wireless transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse-waveforms and evolved into a mechanical/thermal-sensitive electric rubber-balloon and an electronic blood-vessel. The microtopography-guided and self-assembled conductive patterns offer highly promising methodology and tool for next-generation biomedical devices and various flexible/stretchable (wearable) devices.

Research paper thumbnail of Liquid Crystal Size Selection of Large-Size Graphene Oxide for Size-Dependent N-Doping and Oxygen Reduction Catalysis

ACS Nano, Sep 2, 2014

Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic li... more Graphene oxide (GO) is aqueous-dispersible oxygenated graphene, which shows colloidal discotic liquid crystallinity. Many properties of GO-based materials, including electrical conductivity and mechanical properties, are limited by the small flake size of GO. Unfortunately, typical sonochemical exfoliation of GO from graphite generally leads to a broad size and shape distribution. Here, we introduce a facile size selection of large-size GO exploiting liquid crystallinity and investigate the size-dependent N-doping and oxygen reduction catalysis. In the biphasic GO dispersion where both isotropic and liquid crystalline phases are equilibrated, large-size GO flakes (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;20 μm) are spontaneously concentrated within the liquid crystalline phase. N-Doping and reduction of the size-selected GO exhibit that N-dopant type is highly dependent on GO flake size. Large-size GO demonstrates quaternary dominant N-doping and the lowest onset potential (-0.08 V) for oxygen reduction catalysis, signifying that quaternary N-dopants serve as principal catalytic sites in N-doped graphene.

Research paper thumbnail of Flexible Magnetic Microtubules Structured by Lipids and Magnetic Nanoparticles

ACS Applied Materials & Interfaces, May 11, 2009

This study presents a microtubule that responds to a magnetic field. We made such a structure by ... more This study presents a microtubule that responds to a magnetic field. We made such a structure by incorporating iron oxide nanoparticles during the preparation of the microtubule. We found that the microtubule stretches its body when the magnetic field is applied and easily aligns with the direction of the applied magnetic field by rotating its body. When the magnetic field is removed, it loses its orientation and goes back to its original state by contraction. From the analysis of its magnetic response, we estimated that the magnetic microtubule had an elastic modulus of 33 MPa. Further analysis showed that the stretching and contracting of its body are due to its flexibility.

Research paper thumbnail of Improved stability of liposome in oil/water emulsion by association of amphiphilic polymer with liposome and its effect on bioactive skin permeation

Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2007

In this study, we demonstrated that the stability of phosphatidylcholine (PC)-cholesterol (Chol) ... more In this study, we demonstrated that the stability of phosphatidylcholine (PC)-cholesterol (Chol) liposomes can be improved in oil in water (o/w) emulsion by association of amphiphilic polyelectrolyte, poly(methacrylic acid-co-stearyl methacrylate) with PC–Chol liposomes. Differential scanning calorimetry and photocorrelation spectroscopy results showed that the polymer-associated liposomes were more stable than the PC–Chol liposomes when mixed with the o/w emulsion. This difference

Research paper thumbnail of Effect of a Surfactant in Microcapsule Synthesis on Self-Healing Behavior of Capsule Embedded Polymeric Films

Polymers, Jun 17, 2018

Recently, there has been increased interest in self-healing membranes containing functional micro... more Recently, there has been increased interest in self-healing membranes containing functional microcapsules in relation to challenges involving water treatment membranes. In this study, a self-healing membrane has been prepared by incorporating microcapsules with a polyurethane (PU) shell and a diisocyanate core in a poly(ether sulfone) (PES) membrane. Depending on the characteristics of the microcapsule, to precisely quantify the self-healing behavior and performance of the produced microcapsule embedded membranes, it is important to understand the effect of a used surfactant on microcapsule synthesis. It is noteworthy that mixed surfactants have been employed to control and tailor the size and morphology of microcapsules during the synthetic process, and the surfactant system employed was one of the most dominant parameters for affecting the healing capability of microcapsule embedded membranes. Various techniques including microscopy (optical and electron), thermal analyses (DSC and TGA), and water flux measurements have been employed. This article provides essential and important information for future research into the subtle relation between microcapsule properties with varied synthetic parameters and the self-healing behavior of membrane.

Research paper thumbnail of Carbon: 25th Anniversary Article: Chemically Modified/Doped Carbon Nanotubes & Graphene for Optimized Nanostructures & Nanodevices (Adv. Mater. 1/2014)

Research paper thumbnail of One-pot microfluidic fabrication of graphene oxide-patched hollow hydrogel microcapsules with remarkable shell impermeability

Chemical Communications, 2015

Research paper thumbnail of Ultrafast Interfacial Self-Assembly of 2D Transition Metal Dichalcogenides Monolayer Films and Their Vertical and In-Plane Heterostructures

ACS Applied Materials & Interfaces, Dec 28, 2016

Cost effective scalable method for uniform film formation is highly demanded for the emerging app... more Cost effective scalable method for uniform film formation is highly demanded for the emerging applications of 2D transition metal dichalcogenides (TMDs). We demonstrate a reliable and fast interfacial self-assembly of TMD thin films and their heterostructures. Large-area 2D TMD monolayer films are assembled at air-water interface in a few minutes by simple addition of ethyl acetate (EA) onto dilute aqueous dispersions of TMDs. Assembled TMD films can be directly transferred onto arbitrary nonplanar and flexible substrates. Precise thickness controllability of TMD thin films, which is essential for thickness-dependent applications, can be readily obtained by the number of film stacking. Most importantly, complex structures such as laterally assembled 2D heterostructures of TMDs can be assembled from mixture solution dispersions of two or more different TMDs. This unusually fast interfacial self-assembly could open up a novel applications of 2D TMD materials with precise tunability of layer number and film structures.

Research paper thumbnail of Nanosized Emulsions Stabilized by Semisolid Polymer Interphase

Langmuir, Aug 17, 2010

We introduce a new approach for stabilizing oil-in-water nanoemulsions using a semisolid interpha... more We introduce a new approach for stabilizing oil-in-water nanoemulsions using a semisolid interphase formed by the phase separation of amphiphilic block copolymers from the organic phase. This system is illustrated using an amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL), with commonly used oils. PEO-b-PCL can be miscible with oil at elevated temperatures (70-80°C); however, polymer/oil demixing occurs as the temperature drops below the melting temperature of PEO-b-PCL (∼55°C). A homogeneous polymer/oil mixture was dispersed in water at 80°C to generate embryonic emulsions, and then the emulsion size was reduced to a nanometer range through microfluidic homogenization. The structure of the generated nanoemulsions is irreversibly frozen as they are cooled down to ambient temperature. The nanoemulsions stabilized by PEO-b-PCL show the excellent colloidal stability against thermal and chemical stresses, exhibiting no significant changes in the size distribution during incubation for 4 months at ambient temperature or 10 days at 60°C. This study demonstrates that PEO-b-PCL is an attractive emulsifying material for practical nanoemulsion formulations requiring structural stability under a broad range of conditions.

Research paper thumbnail of Silicone oil emulsions stabilized by semi-solid nanostructures entrapped at the interface

Journal of Colloid and Interface Science, Nov 1, 2010

Oil-in-water (O/W) emulsions are typically stabilized using water-soluble surfactants, which anch... more Oil-in-water (O/W) emulsions are typically stabilized using water-soluble surfactants, which anchor to the surface of oil droplets dispersed in an aqueous solution. The structure of the anchored surfactants is often susceptible to physical and chemical stresses because of their highly mobile properties. Here we introduce a new approach to prepare stable silicone oil emulsions under various external stresses using a water-insoluble amphiphilic block copolymer, poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL). Above the melting temperature (around 60 degrees C) of the hydrophobic segment (PCL), PEO-b-PCL can be dissolved in silicone oil. When the polymer/oil mixture is dispersed in water, PEO-b-PCL is irreversibly reorganized into solid nanostructures at the interface of the aqueous/organic phases. The resulting interfacial structures provide a robust physical barrier to the emulsion coarsening processes. Accordingly, the prepared emulsions exhibit excellent structural tolerance against external stresses, including variations in pH, ionic strength, and temperature.

Research paper thumbnail of A Simple Evaporation Method for Large-Scale Production of Liquid Crystalline Lipid Nanoparticles with Various Internal Structures

ACS Applied Materials & Interfaces, Aug 25, 2015

Research paper thumbnail of Transdermal delivery of mixnoxidil with block copolymer nanoparticles

Journal of Controlled Release, Jul 7, 2004

We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration ... more We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration of minoxidil in vitro and in vivo. Self-assembled 40-and 130-nm nanoparticles, both containing minoxidil, were prepared by solvent evaporation of poly(q-caprolactone)-block-poly(ethyleneglycol) and were applied onto the skin of both hairy and hairless guinea pigs in the Franz diffusion cell. In hairy guinea pig skin, the permeation of the minoxidil that incorporated in 40-nm nanoparticles was 1.5fold higher in the epidermal layer and 1.7-fold higher in the receptor solution than that of 130-nm nanoparticles. Nanoparticle size dependence on the permeation behavior of minoxidil was not observed for hairless guinea pig skin in either the epidermal layer or the receptor solution. Phospholipid liposomes and ethanol-water admixture, on the other hand, containing the same amount of minoxidil did not show differences in the amount of permeation irrespective of the existence of hair follicles. Confocal microscopy coupled with in vivo and in vitro skin permeation results demonstrated that nanoparticles containing solutes penetrated mainly via shunt routes like hair follicles, resulting in skin absorption of solutes.

Research paper thumbnail of The skin-permeation-enhancing effect of phosphatidylcholine: caffeine as a model active ingredient

PubMed, Jan 4, 2003

Phospholipids or liposomes are recognized to have skin permeation enhancing ability, although the... more Phospholipids or liposomes are recognized to have skin permeation enhancing ability, although their mechanisms are still controversial. The aim of this study was to establish a method of increasing the skin permeation of active ingredients, using phosphatidylcholine as a permeation enhancer. Caffeine was used as a model active ingredient and in vitro skin penetration experiments were performed using Franz-type diffusion cells to determine the amount of absorbed caffeine. Lipid vesicles were prepared by the microfluidization process. The encapsulation efficiency of caffeine was found to be very low due to the instability of the liposome structure and the water solubility of caffeine. However, the amount of absorbed caffeine was nearly independent of the encapsulation efficiency and the vesicle size, but increased with the increase of phosphatidylcholine concentration. These results indicated that phosphatidylcholine could act as a penetration enhancer, irrespective of its presence in vesicular form or solubilized form.

Research paper thumbnail of Case study on stability analysis of large rock slopes by stereophotogrammetry in highway construction project

Research paper thumbnail of 25th Anniversary Article: Chemically Modified/Doped Carbon Nanotubes & Graphene for Optimized Nanostructures & Nanodevices

Advanced Materials, Oct 14, 2013

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real‐... more Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real‐life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.