• 한국인쇄학회지
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• 제18권2호
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• pp.41-54
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• 2000

가시광을 선택적으로 반사하는 광 응답성 코레스테릭 액정을 조제하고, 그 선택적 반사파장의 광화학적 변조를 시도함으로서 포토닉스(Photonices) 재료로서의 가능성을 검토했다. 고유의 선택 반사파장의 변조는 아조벤젠 유도체의 트란스(trans)·시스(cis)간의 광이성화에 의해 상전이 온도와 칼라의 변화와 함께 가역적으로 제어되어질 수 있었다. 또한 선택 반사파장의 변화에 수반되는 반사율의 변화는 코레스테릭 액정과 검출광의 광학적 성질에 의해 크게 좌우되어 지고, 반사율의 가역적인 스위칭에 있어서는 검출광에 대한 코레스테릭 액정의 초기 반사파장의 위치는 상반된 스위칭 모드(normal and reverse modes)를 산출하기에 매우 중요한 역할을 담당했다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 1999년도 정기총회 및 춘계 공동 학술발표회
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• pp.149-156
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• 1999

In the United States (U.S.), the monitored natural attenuation (MNA) approach has been used as an alternative remedial option for organic and inorganic compounds retained in soil and dissolved in groundwater. The U.S. Environmental Protection Agency (EPA) defines the MNA as“in-situ naturally-occurring processes include biodegradation, diffusion, dilution, sorption, volatilization, and/or chemical and biochemical stabilization of contaminants and reduce contaminant toxicity, mobility or volume to the levels that are protective of human health and the environment”. The Department of Soil Environment. National Institute Environmental Research (NIER) is in the process for demonstrating the MNA approach as a potential remedial option for the BTEX contaminated site in Uiwang City. The project is charactering the research site in terms of the nature and extend of contamination, biological degradation rate, and geochemical and hydrological properties. The microbial-degradation rate and effectiveness of nutrient and redox supplements will be determined through laboratory batch and column tests. The geochemical process will be monitored for determining the concentration changes of chemical species involved in the electron transfer processes that include methanogenesis, sulfate and iron reduction, denitrification, and aerobic respiration. Through field works, critical soil and hydrogeologic parameters will be acquired to simulate the effects of dispersion, advection, sorption, and biodegradation on the fate and transport of the dissolved-phase BTEX plume using Bioplume III model. The objectives of this multi-years research project are (1) to evaluate the MNA approach using the BTEX contaminated site in Uiwang City, (2) to establish a standard protocol for future application of the approach, (3) to investigate applicability of the passive approach as a secondary treatment remedy after active treatments. In this presentation, the overall picture and philosophy behind the MNA approach will be reviewed. Detailed discussions of the site characterization/monitoring plans and risk-based decision-making processes for the demonstration site will be included.

• 한국재료학회지
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• 제21권12호
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• pp.639-643
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• 2011

Zinc oxide as an optoelectronic device material was studied to utilize its wide band gap of 3.37 eV and high exciton biding energy of 60 meV. Using anti-site nitrogen to generate p-type zinc oxide has shown a deep acceptor level and low solubility. To increase the nitrogen solubility in zinc oxide, group 13 elements (aluminum, gallium, and indium) was co-added to nitrogen. The effect of aluminum on nitrogen solubility in a $3{\times}3{\times}2$ zinc oxide super cell containing 72 atoms was investigated using density functional theory with hybrid functionals of Heyd, Scuseria, and Ernzerhof (HSE). Aluminum and nitrogen were substituted for zinc and oxygen sites in the super cell, respectively. The band gap of the undoped super cell was calculated to be 3.36 eV from the density of states, and was in good agreement with the experimentally obtained value. Formation energies of a nitrogen molecule and nitric oxide in the zinc oxide super cell in zinc-rich conditions were lower than those in oxygen-rich conditions. When the number of nitrogen molecules near the aluminum increased from one to four in the super cell, their formation energies decreased to approach the valence band maximum to some degree. However, the acceptor level of nitrogen in zinc oxide with the co-incorporation of aluminum was still deep.

• Bulletin of the Korean Chemical Society
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• 제2권2호
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• pp.71-75
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• 1981

Vacuum ultraviolet photolysis of ethyl bromide was studied at 104.8-106.7 nm (11.4-11.6 eV) in the pressure range of 0.2-18.6 torr at $25^{\circ}$ using an argon resonance lamp with and without additives, i.e., NO and He. Since the ionization potential of $CH_3CH_2Br$ is lower than the photon energy, the competitive processes between the photoionization and the photodecomposition were also investigated. The observations indicated that 50% of absorbed light leads to the former process and the rest to the latter one. In the absence of NO the principal reaction products for the latter process were found to be $CH_4, C_2H_2, C_2H_4, C_2H_6, and C_3H_8$. The product quantum yields of these reaction products showed two strikingly different phenomena with an increase in reactant pressure. The major products, $C_2H_4$ and $C_2H_6$, showed positive effects with pressure whereas the effects on minor products were negative in both cases, i.e., He and reactant pressures. Addition of NO completely suppresses the formation of all products except $C_2H_4$ and reduces the $C_2H_4$ quantum yield. These observations are interpreted in view of existence of two different electronically excited states. The initial formation of short-lived Rydberg transition state undergoes HBr molecular elimination and this state can across over by collisional induction to a second excited state which decomposes exclusively by carbon-bromine bond fission. The estimated lifetime of the initial excited state was ${\sim}4{\times}10^{-10}$ sec. The extinction coefficient for $CH_3CH_2Br$ at 104.8-106.7 nm and $25{\circ}$ was determined to be ${varepsilon} = (1/PL)ln(I_0/I_t) = 2061{\pm}160atm^{-1}cm6{-1}$ with 95% confidence level.

• Bulletin of the Korean Chemical Society
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• 제9권6호
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• pp.368-376
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• 1988

Transition metal PSSA ionomers containing Co(II), Ni(II), Cr(III), Ru(III), and Rh(III) are investigated by IR, Far-IR, UV-Vis and DSC. Reliable IR Spectroscopic criteria are established for assessing the degree of ion-exchange of PSSA ionomers and the local structures around metal cations in them. In the hydrated transition metal PSSA ionomers, the ionic groups are solvated by water molecules and there is no significant interactions between sulfonate group and metal cations. The visible spectra indicated that metal cations are present as [M$(H_2O)_6$]$^{n+}$ with Oh symmetry. Their $T_g$ values increase as the extent of ionic site concentration increases, but there is no direct dependence of $T_g$ on the nature of metal cations or their oxidation states. Thus, the water content in PSSA ionomer is found to have dominant influence on $T_g$ of hydrated transition metal PSSA ionomers. Dehydration of the hydrated transition metal PSSA ionomers results in direct interaction between ionic groups and significant color changes of the ionomers due to the changes of the local structures around metal cations. On the base of spectral data, their local structures are discussed. In case of dehydrated 12.8 and 15.8 mol % transition metal PSSA ionomers, no glass transition is observed in 25-$250^{\circ}C$ region and this is believed to arise from the formation of highly crosslinked structures caused by direct coordination of sulfonate groups of metal cations. In the 6.9 mol % transition metal PSSA ionomers, the glass transition is always observed whether they are hydrated or dehydrated and this is though to be caused by the sufficient segmental mobility of the polymer backbone.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.395-399
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• 1986

Intramolecular proton transfer equilibria of acetamide and methyl carbamate have been studied theoretically by MNDO MO method. For both substrates, carbonyl-O protonated tautomer was found to be the most stable form, the next most stable one being N-protonated form. Gas phase proton transfers take place by the 1,3-proton rearrangement process and in all cases have prohibitively high activation barriers. When however one solvate water molecule participates in the process, the barriers are lowered substantially and the process proceeds in an intermolecular manner through the intermediacy of the water molecule via a triple-well type potential energy surface; three wells correspond to reactant(RC), intermediate(IC) and product complex(PC) of proton donor-acceptor pairs whereas two transition states(TS) have proton-bridge structure. General scheme of the process can be represented for a substrate with two basic centers(heteroatoms) of A and B as, $$ABH\limits^+\;+\;H_2O\;{\to}\;ABH\limits^+{\cdots}{\limits_{RC}}OH_2\;{\to}\;AB{\cdots}H\limits_{TS}^+{\cdots}{\limits_{1}}OH_2\;{\to}\;AB{\cdots}{\limits_{IC}}H\limits^+OH_2\;{\to}\;BA{\cdots}H\limits_{TS}^+{\cdots}{\limits_{2}}OH_2\;{\to}\;BA H\limits^+{\cdots}{\limits_{PC}}OH_2\;{\to}\;BAH\limits^+\;+\;H_2O$$ Involvement of a second solvate water had negligible effect on the relative stabilities of the tautomers but lowered barrier heights by 5∼6 Kcal/mol. It was calculated that the abundance of the methoxy-O protonated tautomer of the methyl carbamate will be negligible, since the tautomer is unfavorable thermodynamically as well as kinetically. Fully optimized stationary points are reported.

• 공업화학
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• 제30권1호
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• pp.23-28
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• 2019

탄소 실의 표면에 코팅 된 3차원 다공성 그래핀으로 구성된 슈퍼커패시터 케이블 소자를 보고하고자 한다. 그래핀의 3D 다공성 구조는 그래핀옥사이드로 코팅된 탄소 실을 사용하여 마이크로웨이브 활성화 방법에 의해 제작하였다. 마이크로파 조사의 사용은 환원제 없이 그래핀옥사이드를 환원된 그래핀옥사이드로 전환시키고 그래핀 시트를 박리 및 다공성 그래핀 시트로 활성화시켰다. 두 개의 와이어 전극을 고분자 겔 전해질과 결합하여 성공적으로 케이블 구조 형태의 슈퍼커패시터 소자를 제작하였다. 슈퍼커패시터 케이블은 매우 유연하기 때문에 다양한 형태의 장치로 변형될 수 있고 섬유 품목으로 통합될 수 있다. 주사 속도 10 mV/s에서 38.1 mF/cm의 높은 정전용량이 얻어졌다. 이용량은 500 mV/s에서 원래 값의 88%를 유지하였다. 장수명특성은 구부러진 형태에서도 10,000회 동안 충전/방전 과정을 반복함으로써 96.5%의 높은 정전용량 유지율을 증명하였다.

• 대한화학회지
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• 제63권2호
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• pp.73-77
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• 2019

${\pi}$-공액계 분자에 대해, density functional theory (DFT) 방법에 기반한 일반적인 삼중항 구조 최적화 방법들, 즉, 시간 의존적 DFT (TD-DFT), Tamm-Dancoff 근사법에 기반한 TD-DFT (TDA-DFT), 그리고 스핀-비제한 DFT (UDFT)에 대한 점검을 수행하였다. 모델 분자로서 1,2,3,4,5-pentacyano-6-phenyl-benzene가 이용되었고, 6-31G(d) 기저 함수와 더불어 여기 상태 계산에 최근 자주 사용되는 에너지 차 조정 영역 분리 functional인 ${\omega}B97X$ functional이 사용되었다. 계산 결과 평형 구조 근처에서, UDFT 최적화된 구조는 TD-DFT 및 TDA-DFT 계산 구조와는 다른 차이점을 보인다. 즉, 보다 안정한 바닥 상태 에너지와 보다 높은 삼중항 여기 에너지가 UDFT 최적화 구조에서 보인다. 본 논문에서는 이러한 차이에 대해 보다 자세히 토의된다.

• 대한화학회지
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• 제63권3호
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• pp.151-159
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• 2019

본 연구는 밀도 범함수 이론(DFT) 가운데 하나인 B3LYP 방법을 $6-31G^{**}$, cc-pVDZ, cc-pVTZ의 바탕함수 집합(basis set)과 함께 사용하여 전자 공여성 분자(D)로 카바졸(carbazol) 그리고 전자 구인성 분자(A)로 dicyanobenzene, diphenyl sulfone, benzonitrile 등의 조합으로 이루어진 열 활성화 지연형광(TADF) 후보 물질에 대하여 분자구조를 최적화하고 진동주파수를 계산하였다. 또한 최적화된 분자 구조에 대하여 HOMO와 LUMO 에너지 차이를 계산하였으며, 나아가 시간 의존 밀도 범함수 이론(TD-DFT)을 사용하여 분자의 최대 흡수 및 방출 파장(${\lambda}_{max}$) 그리고 단일항과 삼중항 들뜬 상태의 에너지 차이(${\Delta}E_{ST}$) 등을 계산하여 열 활성 지연형광(TADF) 소재로서의 가능성을 예측하였다.

• 한국환경보건학회지
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• 제47권1호
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• pp.1-19
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• 2021

Objectives: Phthalates, which are widely used as plasticizers, have been recognized as endocrine disruptors. In the present study, we provided information on the regulation of these chemicals and summarized the information available on their detection and toxicity in children's products and those of their alternatives. Methods: The regulatory frameworks related to phthalates in children's products in Korea, the United States (US), and the European Union (EU) were compared. Data on the detection concentration of 16 phthalates and seven phthalate alternatives that could be used in polyvinyl chloride (PVC) plastic products for children as well as on their toxicity classification and endocrine disruption toxicity were collected from the literature. Results: Korea adopted US and EU chemical standards for six phthalates (DEHP, BBP, DBP, DINP, DIDP, and DNOP), but not others (e.g., DIBP, DPP, DHP, and DCHP). Among the ten phthalates and seven substitutes for which regulatory standards were not determined, DIBP, DHP, DEHA, DIBA, DINA, and DEHT were detected in children's products made from PVC plastic. DIBP and DHP, which have a reproductive toxicity classification of 1B, were frequently detected in PVC toys. The reproductive toxicity, estrogenicity, and anti-androgenic activity of the unregulated phthalates and their alternatives have been reported in diverse in vitro and in vivo assays. Conclusion: The use of unregulated phthalates and their substitutes in children's products is increasing. Further monitoring and toxicological information on phthalate alternatives is required to develop proper management plans.