• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.8.1-8.1
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• 2011

Nanocrystalline titanium dioxide ($TiO_2$) materials have been widely used as an electron collector in DSSC. This is required to have an extremely high porosity and surface area such that the dye can be sufficiently adsorbed and be electronically interconnected, resulting in the generation of a high photocurrent within cells. In particular, their geometrical structures and crystalline phase have been extensively investigated as important issues in improving its photovoltaic efficiency. In this study, we present a new strategy to fabricate a photoelectrode having a periodic structured $TiO_2$ film templated from 1D or 3D polystyrene (PS) microspheres array. Monodisperse PS spheres of various radiuses were used for colloidal array on FTO glasses and two types of photoelectrode structures with different $TiO_2$ materials were investigated respectively. One is the igloo-shaped electrode prepared by $TiO_2$ deposition by RF-sputtering onto 2D microsphere-templated substrates. At the interface between the film and substrate, there are voids formed by the decomposition of PS microspheres during the calcination step. These holes might be expected to play the predominant roles as scattering spherical voids to promote a light harvesting effect, a spacious structure for electrolytes with higher viscosity and effective paths for electron transfer. Additionally the nanocrystalline $TiO_2$ phase prepared by the RF-sputtering method was previously reported to improve the electron drift mobility within $TiO_2$ electrodes. This yields solar cells with a cell efficiency of 2.45% or more at AM 1.5 illumination, which is a very remarkable result, considering its $TiO_2$ electrode thickness (<2 ${\mu}m$). This study can be expanded to obtain higher cell efficiency by higher dye loading through the increase of surface area or multi-layered stacking. The other is the inverse opal photonic crystal electrode prepared by titania particles infusion within 3D colloidal arrays. To obtain the enlargement of ordered area and high quality of crystallinity, the synthesis of titania particles coated with a organic thin layer were applied instead of sol-gel process using the $TiO_2$ precursors. They were dispersed so well in most solvents without aggregates and infused successfully within colloidal array structures. This ordered mesoporous structure provides the large surface area leading to the enough adsorption of dye molecules and have an light harvesting effect due to the photonic band gap properties (back-and-forth reflection effects within structures). A major advantage of this colloidal array template method is that the pore size and its distribution within $TiO_2$ photoelectrodes are determined by those of latex beads, which can be controlled easily. These materials may have promising potentials for future applications of membrane, sensor and so on as well as solar cells.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.31-36
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• 2013

Acetylated Cellulose Ether (ACE), cellulose-based amphiphilic polymer with hydrophilic and hydrophobic, was synthesized and investigated in terms of its solubility and wettability for organic solvents and water. Acetyl group was substituted to the cellulose ether in a hydrophilic polymer by esterification. As a result of FT-IR, the peak corresponding to the hydroxyl group decreased and carboxyl acid peak increased with increasing reaction time and temperature, which signified the increase in the degree of acetylation of the ACE. There were similar thermal decomposition behaviors before and after esterification reaction until $800^{\circ}C$ so that the reaction occurred without significant structural changes of cellulose backbones. The solubility parameter of the ACE had a range of 18.5~26.4, and its viscosity and turbidity were controlled according to the solubility parameter of organic solvents. The ACE showed the hydrophilicity because the contact angle of the ACE was higher than the cellulose ether. These results confirmed that the ACE had the hydrophobicity and hydrophilicity due to the ether which was glucosidic bonding between the glucose units and un-reacted hydroxyl functional groups in the ACE.

• Environmental Mutagens and Carcinogens
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• v.25 no.2
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• pp.60-65
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• 2005

The human solute carrier, SLC41Al, is a $Mg^{2}+$ transporter that is regulated by extracellular magnesium. Although intracellular magnesium plays a fundamental role in cellular metabolism, little is known about how $Mg^{2}+$ is taken up and controlled by cells. Magnesium plays a fundamental role in cellular metabolism so that its control within the body is critical. Magnesium homeostasis is principally a balance between intestinal absorption of dietary magnesium and renal excretion of urinary magnesium. The kidney, mainly the distal convoluted tubule, controls magnesium reabsorption. Although renal reabsorption is under the influence of many hormones, selective regulation of magnesium transport is due to intrinsic control involving transcriptional processes and synthesis of transport proteins. Using microarray analysis, identification of the genetic elements involved with this transcriptional control has been begun. SLC41A1(GenBank Accession No. AJ514402), comprises 10 putative transmembrane domains, two of which are highly homologous to the integral membrane part of the prokaryote transports $Mg^{2}+$ and other divalent cations $Sr^2+,\;Zn^2+,\;Cu^2+,\;Fe^2+,\;Co^2+,\;Ba^2+,\;and\;Cd^2+,\;but\;not\;Ca^2+,\;Mn^2+,\;and\;Ni^2+.$ Transport of $Mg^{2}+$ by SLC41Al is rheogenic, voltage dependent, and not coupled to Na or Cl. Expressed SLC41Al transports a range of other divalent cations: $Mg^{2+},\;Sr^{2+},\;Zn^{2+},\;Cu^{2+},\;Fe^{2+},\;Co^{2+},\;Ba^{2+},\;and\;Cd^{2+}$. The divalent cations $Ca^{2+},\;Mn^{2+},\;and\;Ni^{2+}$and the trivalent ion $Gd^{3+}$ did not induce currents nor did they inhibit $Mg^{2+}$ transport. The nonselective cation $La^{3+}$ abolishes $Mg^{2+}$ uptake. Computer analysis of the SLC41Al protein structure reveals that it belongs to MgtE protein family & suggested that the human solute carrier, SLC41Al, might be a eukaryotic $Mg^{2+}$ transporter closely related $(60-70\%)$ protein encoded by SLC41A2 is a $Mg^{2}+$ transporter that might be involved in magnesium homeostasis in epithelial cells also transports a range of other divalent cations: $Ba^2,\;Ni^2,\;CO^2,\;Fe^2,\;or\;Mn^2,\;but\;not\;Ca^2,\;Zn^2,\;or\;Cu^{2+}$ that may have related functional properties.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.1-5
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• 2015

Lactic acid, the most widely occurring hydroxy-carboxylic acid, has traditionally been used as food, cosmetic, pharmaceutical, and chemical industries. Even though it has tremendous potential for large scale production and use in a wide variety of applications, high cost lactic acid materials are primarily problems. Lactic acid can be obtained on either by fermentation or chemical synthesis. In recent years, the fermentation approach has become more successful because of the increasing market demand for naturally produced lactic acid. Generally, lactic acid was produced from pure starch or from glucose. As an alternative, biomass which is the most abundant renewable resources on earth have been considered for conversion to readily utilizable hydrolysate. In this study, we conducted the fermentation method to produce L(+)-lactic acid production from pretreated hydrolysate was investigated by Lactobacillus rhamnosus ATCC 10863. The hydrolysate was obtained from pretreatment process of biomass using Ammonia percolation process (AP) followed by enzymatic hydrolysis. In order to effectively enhance lactic acid conversion and product yield, controlled medium, temperature, glucose concentration was conducted under pure glucose conditions. The optimum conditions of lactic acid production was investigated and compared with those of hydrolysate.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.786-791
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• 2016

Spherical graphene balls were fabricated by an aerosol spray drying process after reduced graphene oxide was prepared by the liquid phase reaction using glucose as an environment-friendly reducing agent. Spherical morphology of the as-fabricated particles was observed by FE-SEM analysis. Diffraction patterns of spherical particles were found as graphene by XRD analysis. Sphericity of GB was controlled by the variation of operating temperature, amount of glucose, and addition of $NH_4OH$. Higher sphericity of GB was prepared at higher operating temperature in the presence of $NH_4OH$. As the amount of glucose in the liquid phase reaction increased in the presence of $NH_4OH$, sphericity of GB increased. The highest sphericity of GB was 1.1. GB of higher sphericity showed lower aggregation property than that of lower sphericity. Furthermore, as-prepared GBs were found as a potential electrode material for capacitor.

• Toxicological Research
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• v.21 no.4
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• pp.347-353
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• 2005

Eukaryotic initiation factor 4E (elF4E) is a key element for cap-dependent protein translation controlled by affinity between elF4E and 4E-binding protein 1 (4E-BP1). Rapamycin can also affect protein translation by regulating 4E-BP1 phosphorylation. Tobacco-specific nitrosamine, 4(N-methyl-N-nitrosamino )-1-(3-pyridyl)-1-butanone (NNK) is a strong lung carcinogen, but its precise lung cancer induction mechanism remains unknown. Relative roles of cap-dependent and -independent protein translation in terms of NNK-induced lung carcinogenesis were elucidated using normal human bronchial epithelial cells. NNK concentrations applied in this study did not decrease cell viability. Addition of NNK restored rapamycin-induced decrease of protein synthesis and rapamycin-induced phosphorylation of 4E-BP1, and increased expression levels of mTOR, ERK1/2, p70S6K, and Raf-1 in a concentration-dependent manner. NNK also caused perturbation of normal cell cycle progression. Taken together, NNK might cause toxicity through the combination of restoration of 4E-BP1 phosphorylation and increase of elF4E as well as mTOR protein expression, interruption of Raf1/ERK as well as the cyclin G-associated p53 network. Our data could be applied towards elucidation of the molecular basis for lung cancer treatment.

• Applied Chemistry for Engineering
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• v.29 no.1
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• pp.62-66
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• 2018

Styrenated phenol alkoxylates (SP-A) were prepared from styrenated phenol (SP) and ethylene oxide (EO) under a homogeneous base catalyst. However, to use EO that is difficult to handle, a high-pressure reaction device capable of controlling the reaction process should be used. Additionally, when a homogeneous base catalyst is used, a neutralization process is required to remove residual bases after the reaction, and it is also difficult to separate the catalyst and the product. Therefore, in this study, we report the results of SP-A prepared from the reaction of SP and EC using only heterogeneous base catalysts. The heterogeneous base catalyst was obtained by supporting KOH on $La_2O_3$ and calcintion. Using EC instead of EO, it was possible to produce SP-A under the atmospheric rather than high-pressure reaction condition. Average molecular weights of synthesized SP-A varied greatly depending on reaction conditions. The average molecular weight of SP-A prepared using the $KOH/La_2O_3$ catalyst could be controlled arbitrarily by controlling the reaction temperature and added catalyst and EC amounts.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2342-2348
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• 2014

Poly(lactic-co-glycolic acid) (PLGA) were grafted to both ends of Pluronic$^{(R)}$ F68 ($(EO)_{75}(PO)_{30}(EO)_{75}$) triblock copolymer to produce poly{(lactic acid)$_m$-co-(glycolic acid)$_n$}-b-poly(ethylene oxide)$_{75}$-b-poly(propylene oxide)$_{30}$-b-poly(ethylene oxide)$_{75}$-b-poly{(lactic acid)$_m$-co-(glycolic acid)$_n$} (PLGA-F68-PLGA) pentablock copolymers. Molecular weights of PLGA blocks were controlled and five kinds of pentablock copolymers with different PLGA block lengths were synthesized using in-situ ring-opening polymerization of D,L-lactide and glycolide with tin(II) 2-ethylhexanoate ($Sn(Oct)_2$) catalyst. PLGA-F68-PLGA pentablock copolymers were characterized by $^1H$- and $^{13}C$-NMR, GPC, and TGA. The numbers (2m, 2n) of repeating units for lactic acid and glycolic acid inside PLGA segments were obtained as (48, 17), (90, 23), (125, 40), (180, 59), and (246, 64), with $^1H$-NMR measurement. From NMR data, the resultant molecular weights were determined in the range of 12,700-29,700, which were similar to those obtained from GPC. Polydispersity index was increased in the range of 1.32-1.91 as the content of PLGA blocks increased. TG and DTG thermograms showed discrete degradation traces for PLGA and F68 blocks, which indicate the weight fractions of PLGA blocks in pentablock copolymers can be calculated by TG profile and it is possible to remove PLGA block selectively. Hydrodynamic radius and radius of gyration of pentablock copolymer micelle were obtained in the range of 46-68 nm and 31-49 nm, respectively, in very dilute (i.e. 0.005 wt %) aqueous solution of THF:$H_2O$ = 10:90 by volume at $25^{\circ}C$.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.698-706
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• 2019

Over the last few decades, there have been a lot of efforts to develop soft actuators, which can be external stimuli-responsive and applied to the human body. In order to fabricate medical soft actuators with a dynamic precision control, the 3D crosslinked poly(acrylic acid) (PAAc)/poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogels were synthesized in this study by using a radiation technique without noxious chemical additives or initiators. After irradiation, all hydrogels showed high gel fraction over 75% and the ATR-FTIR spectra indicated that PAAc/PVA/PEG hydrogels were successfully synthesized. In addition, the gel fraction, equilibrium water content, and compressive strength were measured to determine the change in physical properties of PAAc/PVA/PEG hydrogels according to the irradiation dose and content ratio of constituents. As the irradiation dose and amount of poly(ethylene glycol) diacrylate (PEGDA) increased, the PAAc/PVA/PEG hydrogels showed a high crosslinking density and mechanical strength. It was also confirmed that PAAc/PVA/PEG hydrogels responded to electrical stimulation even at a low voltage of 3 V. The bending behavior of hydrogels under an electric field can be controlled by changing the crosslinking density, ionic group content, applied voltage, and ionic strength of swelling solution.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.9-17
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• 2017

$K_2Ti_6O_{13}$ whisker have been synthesized by hydrothermal process at low temperature and pressure condition. The average length of the synthesized $K_2Ti_6O_{13}$ whisker was about in the range of 300 nm to $1.5{\mu}m$. The average diameter of the synthesized $K_2Ti_6O_{13}$ whisker was 15 nm to 60 nm. The aspect ratio of the synthesized $K_2Ti_6O_{13}$ whisker was below 12. The average length and diameter of the synthesized $K_2Ti_6O_{13}$ whisker can be controlled by reaction temperature and time, KOH molar ratio. $K_2Ti_6O_{13}$ whisker was synthesized from more than $210^{\circ}C$ and 4 h at reaction temperature and time. The length of the whisker is increased with increasing reaction temperature. Characterization of the synthesized $K_2Ti_6O_{13}$ whisker was carried out using the XRD and FE-SEM.