• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4185-4190
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• 2011

The nucleophilic substitution reactions of ethylene phosphorochloridate (1c) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $5.0^{\circ}C$. The anilinolysis rate of 1c involving a cyclic five-membered ring is four thousand times faster than its acyclic counterpart (1a: diethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (${\Delta}S^{\neq}=+30\;cal\;mol^{-1}K^{-1}$ compared to negative value of 1a (${\Delta}S^{\neq}=-45\;cal\;mol^{-1}K^{-1}$) over considerably unfavorable enthalpy of activation of 1c (${\Delta}H^{\neq}=27.7\;kcal\;mol^{-1}$) compared to 1a (${\Delta}H^{\neq}=8.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. The free energy correlations exhibit biphasic concave upwards for substituent X variations in the X-anilines with a break point at X = 3-Me. The deuterium kinetic isotope effects are secondary inverse ($k_H/k_D$ < 1) with the strongly basic anilines and primary normal ($k_H/k_D$ > 1) with the weakly basic anilines and rationalized by the TS variation from a dominant backside attack to a dominant frontside attack, respectively. A concerted $S_N2$ mechanism is proposed and the primary normal deuterium kinetic isotope effects are substantiated by a hydrogen bonded, four-center-type TS.

• 한국응용과학기술학회지
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• 제31권4호
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• pp.602-611
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• 2014

양쪽성 계면활성제인 dodecyldimethyl(3-sulfopropyl)ammonium hydroxide(LSB, $CH_3(CH_2)_{11}N^+(CH_3)_2(CH_2)_3SO{_3}^-$)와 LSB/Tween-20, LSB/Tween-40, LSB/Tween-80 및 LSB/DTAB, LSB/TTAB, LSB/CTAB 혼합계면활성제의 임계미셀농도(CMC)값을 284 K에서 312 K의 온도범위에서 UV/Vis 분광광도법으로 측정하였다. 열역학적 연구를 위해 온도의 변화가 미셀화에 어떤 영향을 미치는지를 분석하였다. 계산한 결과 측정범위 내에서 미셀화에 따른 깁스 자유에너지값은 측정범위 내에서 모두 음의 값을 나타내었다. 한편 엔탈피값은 Tween-20에서는 양의 값을 그리고 다른 계면활성제에서는 음의 값을 나타내었다. 엔트로피값은 측정한 온도범위 내에서 모두 양의 값을 나타내었다. 또한 모든 열역학 함수값들은 온도와 알킬-그룹의 길이에 따라 큰 변화를 보였다.

• 대한기계학회논문집
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• 제15권6호
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• pp.2189-2205
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• 1991

본 연구에서는 혼합냉매의 열역학적 물성치를 정확하게 예측하기 위하여 척력 과 인력항으로 된 간단한 형태의 상태방정식을 택하고 이를 이용하여 순수성분에 대한 열역학적 물성치 자료와 혼합냉매에 대한 기액평형상태 자료를 이용하여 혼합물에 대 한 열역학적 물성치를 보다 더욱 정확하게 예측 할 수 있는 방법에 관해 연구하고자 한다.혼합냉매에 대한 상태방정식과 이상기체 상태의 비열자료를 기초로 열역학적 관계식을 이용하여, 압력-엔탈피, 온도-엔트로피 관계를 공식화하며, 혼합냉매에 대한 열펌프 및 냉동사이클 해석에 필요한 자료를 제시한다.

• 청정기술
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• 제20권3호
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• pp.290-297
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• 2014

본 연구에서는 활성탄을 사용하여 coomassi brilliant blue G (CBBG)염료를 흡착하는데 필요한 흡착평형과 흡착동역학 및 열역학 파라미터들에 대하여 조사하였다. 등온흡착평형관계로 부터 Langmuir 식과 Freundlich 식의 분리계수를 평가하여 활성탄에 의한 CBBG의 흡착조작이 유효한 처리방법이 될 수 있음을 알았고, Dubinin-Radushkevich 식으로부터 흡착공정이 물리흡착공정임을 알았다. 흡착공정에 대한 동력학적 해석을 통해 흡착반응은 유사이차반응속도식이 유사일차반응속 도식에 비해 일치도가 높은 것으로 나타났으며, 입자내확산이 흡착공정의 지배단계임을 알았다. 유사이차반응속도식을 적용한 열역학적 해석을 통해 평가된 엔탈피 변화값(406.12 kJ/mol)으로부터 흡착공정이 흡열반응으로 진행됨을 알았다. 또한 엔트로피 변화값(1.66 kJ/mol K)은 흡착공정의 무질서도가 증가한다는 것을 나타내었다. 온도가 올라갈수록 자유에너지 값이 감소하는 경향을 보인 것은 활성탄에 대한 CBBG의 흡착반응은 온도가 올라갈수록 자발성이 높아지는 것으로 판단되었다.

• 대한화학회지
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• 제35권1호
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• pp.64-69
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• 1991

아세토니트릴 용매 중에서 p-methylphenacyl arenesulfonate와 피리딘의 반응을 1∼2000 bars 및 35∼55$^{\circ}C$에서 전기전도도법으로 측정하였다. 반응속도는 온도와 압력의 증가에 따라 증가하였으며, 이탈기에 전자받개 치환기가 도입됨에 따라 증가하였다. 활성화엔탄피, 엔트로피 및 부피로부터 이 반응은 전반적으로 S$_N$2 반응으로 진행되나 압력이 증가함에 따라 C${\cdots}$O 결합분열이 더욱 진전된 dissociative S$_N$2 반응으로 진행됨을 알 수 있었다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권7호
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• pp.275-281
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• 2003

$Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ and $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$:$Co^{2+}$ single crystals were grown by CTR method. The grown single crystals have defect chalcopyrite structure with lattice constant a=5.5966$\AA$, c=10.8042$\AA$ for the pure, a=5.6543$\AA$, c=10.8205$\AA$ for the Co-doped single crystal, respectively. The optical energy band gap was given as indirect band gap. The optical energy band gap was decreased according to add of Co-impurity Temperature dependence of optical energy band gap was fitted well to the Varshni equation. From this relation, we can deduced the entropy, enthalpy and heat capacity. Also, we can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_{d}$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

• 한국분말재료학회지
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• 제29권3호
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• pp.213-218
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• 2022

This study investigates the interfacial reaction between powder-metallurgy high-entropy alloys (HEAs) and cast aluminum. HEA pellets are produced by the spark plasma sintering of Al_0.5CoCrCu_0.5FeNi HEA powder. These sintered pellets are then placed in molten Al, and the phases formed at the interface between the HEA pellets and cast Al are analyzed. First, Kirkendall voids are observed due to the difference in the diffusion rates between the liquid Al and solid HEA phases. In addition, although Co, Fe, and Ni atoms, which have low mixing enthalpies with Al, diffuse toward Al, Cu atoms, which have a high mixing enthalpy with Al, tend to form Al-Cu intermetallic compounds. These results provide guidelines for designing Al matrix composites containing high-entropy phases.

• Preventive Nutrition and Food Science
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• 제20권3호
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• pp.215-220
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• 2015

The moisture sorption isotherms of vacuum-dried edible green alga (Capsosiphon fulvescens) powders were determined at 25, 35, and $45^{\circ}C$ and water activity ($a_w$) in the range of 0.11~0.94. An inversion effect of temperature was found at high water activity (>0.75). Various mathematical models were fitted to the experimental data, and Brunauer, Emmett, and Teller model was found to be the most suitable model describing the relationship between equilibrium moisture content and water activity (<0.45). Henderson model could also provide excellent agreement between the experimental and predicted values despite of the intersection point. Net isosteric heat of adsorption decreased from 15.77 to 9.08 kJ/mol with an increase in equilibrium moisture content from 0.055 to $0.090kg\;H_2O/kg$ solids. The isokinetic temperature ($T_{\beta}$) was 434.79 K, at which all the adsorption reactions took place at the same rate. The enthalpy-entropy compensation suggested that the mechanism of the adsorption process was shown to be enthalpy-driven.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.184-193
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• 2020

One of the technical methods to increase the volumetric energy density of hydrogen is to pressurize the gaseous hydrogen and then contain it in a rigid vessel. Especially for automotive systems, the compressed hydrogen storage can be found in cars as well as at refueling stations. During the charging the pressurized hydrogen into a vessel, the temperature increases with the amount of stored hydrogen in the vessel. The temperature of the vessel should be controlled to be less than a limitation for ensure stability of material. Therefore, the accurate estimation of temperature is of significance for safely storing the hydrogen. In this work, three well-known cubic equations of state (EOSs) were adopted to examine the accuracy in regenerating thermodynamic properties of hydrogen within the temperature and pressure ranges for the compressed hydrogen storage. The formulations representing molar volume, internal energy, enthalpy, and entropy were derived for Redlich-Kwong (RK), Soave-Redlioch-Kwong (SRK), and Peng-Robinson (PR) EOSs. The calculated results using the EOSs were compared with literature data given by NIST. It was revealed that the accuracies of RK and SRK EOSs were satisfactorily compatible and better than the results by PR EOS.

• Bulletin of the Korean Chemical Society
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• 제30권5호
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• pp.1031-1034
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• 2009

Fluorescence of quinolones including norfloxacin, ciprofloxacin and S- and R-ofloxacin is quenched upon association with single and double-stranded DNA (ss- and ds-DNA). The ratios of fluorescence intensity in the presence of DNA to its absent were plotted with respect to the DNA concentration to construct the Stern-Volmer plot. The slope of the Stern-Volmer plot become larger as the temperature is lowered, ensuring that the fluorescence quenching is static process, i.e., the fluorescence is quenched by formation of the non-fluorescent complex between quinolone and DNA. In the static quenching mechanism, the quenching constant which is equivalent to the slope of the Stern-Volmer plot, is considered as the equilibrium constant for the association of quinolones and DNA. From the temperature-dependent equilibrium constant, ${\Delta}H^0\;and\;{\Delta}S^0$ was obtained using the van’t Hoff relation. In general, association of the quinolone with ds- as well as ss-DNA is energetically favorable (an exothermic) process while the entropy change was unfavorable. Due to the steric effect of the substituents, the effect of the quinolone ring is smaller on the ss-DNA compared to ds-DNA.