• Composites Research
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• v.29 no.4
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• pp.145-150
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• 2016

Polyvinylidene fluoride (PVDF) as a representative polymer with the piezoelectric property has been studied since the 1960s. Crystalline structure of poly(vinylidene fluoride) polymer is composed of five different crystal structure of the polymer as a semi-crystalline. Among the various crystal structures, ${\beta}-type$ crystal exhibits a piezoelectricity because the permanent dipoles are aligned in one direction. Generally ${\beta}-form$ crystal structure can be obtained through the transformation of the ${\alpha}-form$ crystal structure by the stretching and it can increase the amount through the after treatment as poling process after stretching. ${\beta}-form$ crystal structure the PVDF fibers produced by wet spinning is formed through a diffusion mechanism of a polar solvent in the coagulation bath. However, it has a disadvantage that the diffusion path of the solvent remains as pores in the fiber because the fiber solidification occurs simultaneously with the diffusion of the polar solvent. These pores play a role in reducing effect of poling process owing to effect of disturbances acting on the polarization by the electric field. In this work, the drying method using the microwave was introduced to remove more effectively the residual solvent and the pore within PVDF fibers produced through wet-spinning process and piezoelectric PVDF fibers was produced by transformation of the remaining ${\alpha}$ form crystal structure into ${\beta}-crystal$ structure through the stretching process.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.189-195
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• 2009

$\beta-Ga_{2}O_{3}$ nanorods were synthesized by chemical vapor deposition method using nickel-oxide nanoparticle as a catalyst and gallium metal powder as a source material. The average diameter of nanorods was around 160 nm and the average length was $4{\mu}m$. Also, we confirmed that the synthesis of nanorods follows the vapor-solid growth mechanism. From the results of X-ray diffraction and HR-TEM observation, it can be found that the synthesized nanorods consisted of a typical core-shell structure with single-crystalline $\beta-Ga_{2}O_{3}$ core with a monoclinic crystal structure and an outer amorphous gallium oxide layer. Li/$\beta-Ga_{2}O_{3}$ nanorods cell delivered capacity of 867 mAh/g-$\beta-Ga_{2}O_{3}$ at first discharge. Although the Li/$\beta-Ga_{2}O_{3}$ nanorods cell showed low coulombic efficiency at first cycle, the cell exhibited stable cycle life property after fifth cycle.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.1
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• pp.5-14
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• 2023

In this study, LiDAR-reflective black hollow-structured silica/titania(B-HST) materials are successfully synthesized by employing the NaBH₄ reduction and etching method on silica/titania core/shell(STCS) materials, which also effectively enhance near-infrared(NIR) reflectance. Moreover, core-etched supernatant solutions are collected and recycled for the synthesis of extracted silica(e-SiO₂) process, which successfully applies as filler materials for semiconductor epoxy molding compound(EMC). In detail, B-HST materials, fabricated by the sequential experimental steps of sol-gel, reduction, and sonication-mediated etching method, manifest blackness(L^*) of 13.2 similar to black paint and excellent NIR reflectance(31.1%). Consequently, B-HST materials are successfully prepared as LiDAR-reflective black materials. Additionally, core-etched supernatant solution with silanol precursors are employed for synthesis of homogeneous silica filler materials via sol-gel method. As-synthesized silica fillers are incorporated with epoxy resin and carbon black for the preparation of semiconductor EMC. Experimentally synthesized EMC exhibits comparable mechanical-chemical properties to commercial EMC. Conclusively, this study successfully proposes designing procedure and practical experimental method for simultaneously synthesizing the NIR-reflective black materials for self-driving vehicles and EMC materials for semiconductors, which are materials suitable for the industrial 4.0 era, and presented their applicability in future industries.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.1
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• pp.41-46
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• 2011

The artificial aggregates (AAs) composing of 2 wastes, coal bottom ash and dredged soil (7 : 3, weight ratio) were fabricated as a function of red mud contents,0~30 wt% using direct sintering method at $1050{\sim}1250^{\circ}C$ for 10 min, and those physical properties were evaluated. Especially, in order to analyze the red mud addition effect on the bloating phenomenon of AAs manufactured, the specific gravity and water absorption were measured and studied linked with the microstructural observation results. The lightening of AAs was enhanced due to increased bloating with increasing temperature and red mud contents. The AAS sintered at $1050{\sim}1150^{\circ}C$ showed well-developed black-coring structure, but for the specimens containing red mud sintered over $1200^{\circ}C$ generated excessive liquid and gas caused by reduction of $Fe_2O_3$, thus the black-coring part was gradually burst open out of shell of AAs. Particularly, all specimens containing 30 wt% red mud was burst up when sintered over $1100^{\circ}C$. The AAs containing no red mud sintered at $1200^{\circ}C$ had a specific gravity of about 1.2 and those containing 20 wt% had below 1.0 which are characters of lightweight aggregate.

• Journal of the Korean Magnetics Society
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• v.27 no.3
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• pp.87-91
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• 2017

Carbon-encapsulated Ni and metal Ni nanoparticles were synthesized by levitational gas condensation (LGC). Methane ($CH_4$) gas was used to coat the surface of the Ni nanoparticles. The Ni particles had a core diameter of 10 nm, and were covered by 2~3 nm thin carbon layers with multi-shells structure.The low magnetization comparing with the Ni nanoparticles without carbon-shell results in the coexistence of nonmagnetic carbon and a large surface spin percentage with disordered magnetization orientation for the nanoparticles. Biginelli reactions in the presence of L-proline and Ni and carbon encapsulated Ni nanoparticles were carried out to change the ratio between stereoisomers. The obtained S-enantiomers for 3,4-dihydropyrimidine (DHPM) using catalysts of Ni, and Ni@C was an excess of about ${\Delta}{\sim}7.4%$ and ${\Delta}{\sim}19.6%$, respectively. The nanopowders were fully recovered using magnet to reuse as a catalyst. The Ni@C was shown at same yield to formation of 3,4-DHPM, though it was recycled for catalyst in the reaction.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.729-732
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• 2012

Herein we report the in-situ synthesis and direct decoration of chalcogenide naoparticles (NPs) onto multiwalled carbon nanotubes (MWCNTs) through an ionic liquid-assisted sonochemical method (ILASM). The as-obtained MWCNT/$BMimBF_4$/CdTe, MWCNT/$BMimBF_4$/ZnTe and MWCNT/$BMimBF_4$/ZnSe nanocomposites were characterized by TEM images and EDS spectra. In particular, the morphologies of nanocomposites such as bump-like, rough, and smooth core-shell structures were strongly influenced by the type of precursors and the interactions with MWCNT. This synthetic strategy opens a new way to directly synthesize and deposit semiconducting NPs (s-NPs) onto CNTs, which consist of binary components obtained from two precursors with different reaction rates.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.246.1-246.1
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• 2014

Over the past several years, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED). In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[1] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QDLEDs, blend of poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo) and poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] are used as hole transporting layer (HTL) to improve hole transporting property. At the operating voltage of 8 V, the QDLED device emitted spectrally orange color lights with high luminance up to 2450 cd/m2, and showed current efficacy of 0.6 cd/A, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.432.2-432.2
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• 2014

Recently, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED)[1]. In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[2] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QD LED, two kinds of hybrid organic materials, [poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo)(F8BT) + poly(N,N'-bis (4-butylphenyl)-N,N'-bis(phenyl)benzidine (poly-TPD)] and [4,4'-N,N'-dicarbazole-biphenyl (CBP) + poly-TPD], were adopted as hole transport layer having high highest occupied molecular orbital (HOMO) level for improving hole transport ability. At a low-operating voltage of 8 V, the device emits orange and red spectral radiation with high brightness up to 2450 and 1420 cd/m2, and luminance efficacy of 1.4 cd/A and 0.89 cd/A, respectively, at 7 V applied bias. Also, the carrier transport mechanisms for the QD LEDs are described by using several models to fit the experimental I-V data.

• Journal of Powder Materials
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• v.24 no.1
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• pp.1-5
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• 2017

We have investigated the washing method of as-synthesized CdSe/ZnS core/shell structure quantum dots (QDs) and the effective surface passivation method of the washed QDs using PMMA. The quantum yield (QY%) of as-synthesized QDs decreases with time, from 79.3% to 21.1%, owing to surface reaction with residual organics. The decreased QY% is restored to the QY% of as-synthesized QDs by washing. However, the QY% of washed QDs also decreases with time, owing to the absence of surface passivation layer. On the other hand, the PMMA-treated QDs maintained a relatively higher QY% after washing than that of the washed QDs that were kept in toluene solution for 30 days. Formation of the PMMA coating layer on CdSe/ZnS QD surface is confirmed by HR-TEM and FT-IR. It is found that the PMMA surface coating, when combined with washing, is useful to be applied in the storage of QDs, owing to its long-term stability.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.217-217
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• 2011

Recently, demand for thermally stable metal nanoparticles suitable for chemical reactions at high temperatures has increased to the point to require a solution to nanoparticle coalescence. Thermal stability of metal nanoparticles can be achieved by adopting core-shell models and encapsulating supported metal nanoparticles with mesoporous oxides [1,2]. However, to understand the role of metal-support interactions on catalytic activity and for surface analysis of complex structures, we developed a novel catalyst design by coating an ultra-thin layer of titania on Pt supported silica ($SiO_2/Pt@TiO_2$). This structure provides higher metal dispersion (~52% Pt/silica), high thermal stability (~600$^{\circ}C$) and maximization of the interaction between Pt and titania. The high thermal stability of $SiO_2/Pt@TiO_2$ enabled the investigation of CO oxidation studies at high temperatures, including ignition behavior, which is otherwise not possible on bare Pt nanoparticles due to sintering [3]. It was found that this hybrid catalyst exhibited a lower activation energy for CO oxidation because of the metal-support interaction. The concept of an ultra-thin active metal oxide coating on supported nanoparticles opens-up new avenues for synthesis of various hybrid nanocatalysts with combinations of different metals and oxides to investigate important model reactions at high-temperatures and in industrial reactions.