• 대한금속재료학회지
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• 제49권8호
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• pp.596-600
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• 2011

Thermal degradation behavior of a $WO_3-TiO_2$ monolithic catalyst was investigated in terms of structural, morphological, and physico-chemical analyses. The catalyst with 4 wt.% $WO_3$ contents were prepared by a wet-impregnation method, and a durability test of the catalysts were performed in a temperature range between $400^{\circ}C$ and $800^{\circ}C$ for 3 h. An increase of thermal stress decreased the specific surface area, which was caused by grain growth and agglomeration of the catalyst particles. The phase transition from anatase to rutile occurred at around $800^{\circ}C$ and a decrease in the Brønsted acid sites was confirmed by structural analysis and physico-chemical analysis. A change in Brønsted acidity can affect to the catalytic efficiency; therefore, the thermal degradation behavior of the $WO_3-TiO_2$ catalyst could be explained by the transition to a stable rutile phase of $TiO_2$ and the decrease of specific surface area in the SCR catalyst.

• Korean Chemical Engineering Research
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• 제61권1호
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• pp.97-108
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• 2023

Two carbonaceous adsorbents CAT and CARBOPAL were tested for reducing the concentration of the three herbicides in water: 2,4-D (2,4-dichlorophenoxyacetic acid), TCP (2,4,6-trichlorophenol) and metolachlor. Textural and chemical characterization of the adsorbents include nitrogen isotherms, FTIR, titration and thermogravimetric analyses. Adsorption was studied in discontinuous adsorption experiments at different pH values. The experimental adsorption isotherms data were fitted to four theoretical models. Adsorbent characterization reveals that CAT has higher micropore area, lower pore diameter and lower acidity than CARBOPAL. The adsorption is a second-order process and the isotherms best fitted to Sips model. The efficiency of the process depends mainly on the charge of the adsorbate for TCP and 2,4-D, but it depends on the charge of the surface for metolachlor. Adsorption capacity is higher on CAT for 2,4-D and TCP (small molecules), and it is higher on CARBOPAL for metolachlor (large molecules). Theoretical calculations clearly support this assumption.

• 폴리머
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• 제29권6호
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• pp.588-592
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• 2005

자외선을 차단할 목적으로, 단일 모재를 사용함으로써 기존 방법이 갖고 있는 차단제의 적층에 따른 두께 증가와 접착제의 반응 온도에 따른 변형 등의 단점을 개선하고자 하였다. 화장품 용기 및 옥외용으로 사용 가능한 고분자 필름(폴리카보네이트) 표면에 이온 조사를 통하여 고분자 표면을 개질하였다. 표면 개질된 필름의 280$\∼$400 nm 사이 자외선 차단 특성, 표면의 화학 및 형태 변화 특성, 자외선에 대한 저항성을 W분광기, FTIR(ATR)과AFM, UV 촉진 내광성 시험기를 이용하여 측정하였다. 분석 결과, 개질된 고분자 필름은 자외선 전 영역을 차단할 수 있었고 이온의 주입량에 따라 차단율을 자유롭게 변화시킬 수 있었다. 이는 이온들의 주입으로 인한 고분자의 표면 화학 변화에 기인한다. 개질된 고분자 표면은 nm수준으로, 별도의 차단제가 필요없는 하나의 모재로, 자외선 차단을 위해 활용 할 수 있으리라 판단된다. 또한 자외선 조사에 따른 고분자의 색 변화 및 자외선 투과 특성 변화가 없음을 확인하여 일상 생활환경에서 지속적인 자외선 차단 방법으로 사용 가능하리라 기대할 수 있었다.

• 한국응용과학기술학회지
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• 제17권4호
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• pp.213-225
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• 2000

Sophorolipids were biosynthesized using a strain of yeast, Torulopsis bombicola ATCC22214. It has been reported that this yeast gives the highest yields for the production of biosurfactant sophorolipids. Hence, this yeast was used in this study. One of the objectives of this study is to increase the yield of the sophorolipid synthesis. To meet this end, basic culture medium was formulated on the basis of literature research to-date. When this medium was used, the increase in yield from 15% to 150% was observed compared to using the media in the literature. To examine how the interfacial characteristics of sophorolipids change with substrate, glucose (the first carbon source) was maintained in the media and after being cultured for three days, the second carbon sources such as alkanes, vegetable oils, alcohols or organic acids were added. The whole broth was extracted twice with ethyl acetate and the extract was analyzed by thin layer chromatograhy(TLC). After qualitative analyses by TLC, surface tensions of sophorolipids were measured by the Wilhelmy plate method and critical micelle concentration(CMC) was determined using these surface tension data. Also, interfacial tensions were measured by the spinning drop method and emulsions of the three-component water/decane/sophorolipid system were tested. Sophorolipids were effective and efficient in terms of surface tension reduction and CMC, but they were ineffective as emulsifiers because emulsions were separated within 30 minutes.

• Elastomers and Composites
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• 제53권3호
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• pp.124-130
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• 2018

Recently, microwaves have been used for desulfurization because they can selectively dissociate C-S and S-S bonds present in vulcanized rubber. In this study, we investigated the changes in structural and physical properties of EPDM (Ethylene propylene diene monomer) rubber by irradiating it with microwaves for different durations. The surface chemical composition of the irradiated EPDM rubber was analyzed by FT-IR, XPS, and EDS analyses. It was confirmed by XPS that C-S and S-S S2p peak heights greatly decreased when microwave irradiation was performed for more than 5 min. In the EPDM sample irradiated with microwaves for 10 min, the number of S-O bonds significantly increased owing to oxidation. As the microwave irradiation time was increased, SEM images showed cracks and voids on the EPDM surface. The 20% decomposition temperature of the EPDM rubber sample was investigated by TGA, and it was found to be about $435.23^{\circ}C$ for the EPDM rubber irradiated for 10 min. The crosslinking density of the EPDM rubber was determined by measuring the degree of swelling, and the highest value was observed for the E5 sample irradiated for 5 min. The degree of swelling of the E10 sample irradiated for 10 min was lower than that of the E5 sample. These results indicate that when irradiated with microwaves for more than a certain time, desulfurization occurs and the side chain of the EPDM rubber dissociates and forms additional crosslinking bonds.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.383-383
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• 2010

Gas-phase hydrogen atoms create a variety of chemical and physical phenomena on Si surfaces: adsorption, abstraction of pre-adsorbed H, Si etching, Si amorphization, and penetration into the bulk lattice. Thermal desorption/evolution analyses exhibited three distinct peaks, including one from the crystalline bulk. It was previously found that thermal-energy gaseous H(g) atoms penetrate into the Si(100) crystalline bulk within a narrow substrate temperature window(centered at ~460K) and remain trapped in the bulk lattice before evolving out at a temperature as high as ~900K. Developing and sustaining atomic-scale surface roughness, by H-induced silicon etching, is a prerequisite for H absorption and determines the $T_s$ windows. Issues on the H(g) absorption to be further clarified are: (1) the role of the detailed atomic surface structure, together with other experimental conditions, (2) the particular physical lattice sites occupied by, and (3) the chemical nature of, absorbed H(g) atoms. This work has investigated and compared the thermal H(g) atom absorptivity of Si(100), Si(111) and Si(110) samples in detail by using the temperature programmed desorption mass spectrometry (TPD-MS). Due to the differences in the atomic structures of, and in the facility of creating atom-scale etch pits on, Si(100), (100) and (110) surfaces, the H-absorption efficiency was found to be larger in the order of Si(100) > Si(111) > Si(110) with a relative ratio of 1 : 0.22 : 0.045. This intriguing result was interpreted in terms of the atomic-scale surface roughening and kinetic competition among H(g) adsorption, H(a)-by-H(g) abstraction, $SiH_3(a)$-by-H(g) etching, and H(g) penetraion into the crystalline silicon bulk.

• Restorative Dentistry and Endodontics
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• 제48권3호
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• pp.26.1-26.12
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• 2023

Objective: This in vitro study aimed to evaluate the effects of different whitening toothpastes on a composite resin during at-home bleaching with 10% carbamide peroxide. Materials and Methods: Sixty samples (7 mm × 2 mm) were used for color and roughness analyses, while another 60 samples (3 mm × 2 mm) were utilized to assess microhardness. The factors analyzed included toothpaste, for which 5 options with varying active agents were tested (distilled water; conventional toothpaste; whitening toothpaste with abrasive agents; whitening toothpaste with abrasive and chemical agents; and whitening toothpaste with abrasive, chemical, and bleaching agents). Brushing and application of whitening gel were performed for 14 days. Surface microhardness (SMH), surface roughness (Ra), and color (ΔL^*, Δa^*, Δb, ΔE^*_ab, and ΔE₀₀) were analyzed. The Ra and SMH data were analyzed using mixed generalized linear models for repeated measures, while the color results were assessed using the Kruskal-Wallis and Dunn tests. Results: Between the initial and final time points, all groups demonstrated significant increases in Ra and reductions in SMH. No significant differences were found between groups for SMH at the final time point, at which all groups differed from the distilled water group. Conventional toothpaste exhibited the lowest Ra, while whitening toothpaste with abrasive agent had the highest value. No significant differences were observed in ΔL^*, Δa^*, and Δb. Conclusions: While toothpaste composition did not affect the color stability and microhardness of resin composite, combining toothbrushing with whitening toothpaste and at-home bleaching enhanced the change in Ra.

• Macromolecular Research
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• 제13권5호
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• pp.446-452
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• 2005

The interactions between the surface of scaffolds and specific cells play an important role in tissue engineering applications. Some cell adhesive ligand peptides including Arg-Gly-Asp (RGD) have been grafted into polymeric scaffolds to improve specific cell attachment. In order to make cell adhesive scaffolds for tissue regeneration, biodegradable nonporous poly(L-lactic acid) (PLLA) films were prepared by using a solvent casting technique with chloroform. The hydrophobic PLLA films were surface-modified by Argon plasma treatment and in situ direct acrylic acid (AA) grafting to get hydrophilic PLLA-g-PAA. The obtained carboxylic groups of PLLA-g-PAA were coupled with the amine groups of Gly-Arg-Asp-Gly (GRDG, control) and GRGD as a ligand peptide to get PLLA-g-GRDG and PLLA-g-GRGD, respectively. The surface properties of the modified PLLA films were examined by various surface analyses. The surface structures of the PLLA films were confirmed by ATR-FTIR and ESCA, whereas the immobilized amounts of the ligand peptides were 138-145 pmol/$cm^2$. The PLLA surfaces were more hydrophilic after AA and/or RGD grafting but their surface morphologies showed still relatively smoothness. Fibroblast adhesion to the PLLA surfaces was improved in the order of PLLA control

• Journal of Microbiology and Biotechnology
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• 제7권3호
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• pp.180-188
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• 1997

Bacillus subtilis C9 was selected by measuring the oil film-collapsing activity and produced biosurfactant in a medium containing glucose as a sole carbon source. The biosurfactant emulsified hydrocarbons, vegetable oils and crude oil, and lowered the surface tension of culture broth to 28 dyne/cm. A biosurfactant, C9-BS produced by B. subtilis C9 was purified by ultrafiltration, extraction with chloroform and methanol, adsorption chromatography, and preparative reversed phase HPLC. Structural analyses, IR spectroscopy, FAB mass spectroscopy, amino acid composition, and NMR analyses, demonstrated that C9-BS was a lipopeptide comprising a fatty acid tail and peptide moiety. The lipophilic part consisting of $C_{14}\;or\;C_{15}$ hydroxy fatty acid was linked to the hydrophilic peptide part, which contained seven amino acids (Glu-Leu-Leu-Val-Asp-Leu-Leu) with a lactone linkage.

• 폴리머
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• 제37권4호
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• pp.437-441
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• 2013

A novel sulfonate flame retardant, 1,3,5,7-tetrakis(phenyl-4-sodium sulfonate)adamantane (FR-A), was successfully synthesized from 1-bromoadamantane in sequential four-step reactions involving Fiedel-Crafts phenylation, sulphonation, hydrolysis, and neutralization. The success of synthesis was confirmed by FTIR spectra, $^1H$ NMR spectra, elemental analyses and mass spectra. The effect of FR-A on the flame retardacy of polycarbonate (PC) has been studied. Limiting oxygen index (LOI) and thermogravimetric analysis (TGA) showed that this novel sulfonate flame retardant had effective flame retardancy on polycarbonate (PC). With a small amount (0.08 wt%) of FR-A, the flame retardancy of PC was improved obviously, which got to UL 94 V-0 rating. TGA and DTA curves demonstrated that the additive raised the degradation rate of PC by promoting the quick formation of an insulating carbon layer on the surface, and confirmed that the flame retardant mechanism of PC/FR-A system was similar to potassium diphenylsulfone sulfonate (KSS).