• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.75-79
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• 1993

The Thermally Stimulated Current(TSC) method has been allied to study the influence of the structural change and interface on the electrical properties of epoxy composites. Three DGBA- MeTHPA matrix model samples mixed different ratios arts silica(SiO$_2$) filled sample and silaln treating-filled sample have been studied. Above room temperature, the relaxation mode ${\alpha}$ peak associated with T$\_$g/ has been located at 110$^{\circ}C$. Below glass transition temperature(T$\_$g/), three relaxation modes are observed in all samples : a ${\beta}$ mode situated at 10$^{\circ}C$, a ${\gamma}$ mode located at -40$^{\circ}C$ and a $\delta$mode appeared in -120$^{\circ}C$, which may be due to segmental motion, side chains, substitution and terminal groups. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the change of the molecular structure and their thermal motion are compared with the relaxation mode and conduction mechanism in TSC spectra through the dielectric properties and FTIR measurements.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.191-196
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• 2008

Kinetic studies of the reactions of a-bromoacetanilides [YC6H4NHC(=O)CH2Br] with substituted benzylamines (XC6H4CH2NH2) have been carried out in dimethyl sulfoxide at 35.0 oC. The Hammett plots for substituent (Y) variations in the substrate (log kN vs. sY) are biphasic concave upwards/downwards with breaks at Y = 4-Cl (sY = 0.23). The Hammett coefficients rY and the cross-interaction constant rXY (= +0.16) are positive for sY 0.23, while the rY values are positive/negative [rY > 0 for X = (4-MeO and 4-Me) and rY < 0 for X = (H, 4-Cl and 3-Cl)] and the rXY (= -1.51) value is negative for sY ³ 0.23. Based on these and other results, the benzylaminolyses of a-bromoacetanilides are proposed to proceed through rate-limiting expulsion of the bromide leaving group from a zwitterionic tetrahedral intermediate, T, with a bridged transition state for s Y 0.23, while the reaction proceeds through concerted mechanism with an enolate-like TS in which the nucleophile attacks the a-carbon for s Y ³ 0.23.

• Bulletin of the Korean Chemical Society
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• v.32 no.9
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• pp.3355-3360
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• 2011

The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $-15.0^{\circ}C$. The studied substrate of 1,2-phenylene phosphorochloridate is cyclic five-membered ring of phosphorus ester, and the anilinolysis rate of 1 is much faster than its acyclic analogue (4: ethyl phenyl chlorophosphate) because of extremely small magnitude of the entropy of activation of 1 compared to 4. The Hammett and Bronsted plots exhibit biphasic concave upwards for substituent X variations in the nucleophiles with a break point at X = 3-Me. The values of deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) change from secondary inverse ($k_H/k_D$ < 1) with the strongly basic anilines to primary normal ($k_H/k_D$ > 1) with the weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the transition state (TS) variation from a predominant backside attack to a predominant frontside attack, in which the reaction mechanism is a concerted $S_N2$ pathway. The primary normal DKIEs are substantiated by a hydrogen bonded, four-center-type TS.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1240-1246
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• 1994

While sintering the Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 system through solid-reaction route, pyrochlore(Pb3Nb4O13) phase while reduces the dielectric constant is inevitably formed. Substitution of Pb(Mg1/3Nb2/3)O3 with PbTiO3 and BaTiO3 can retard the occurrence of pyrochlore phase. The perovskite solid-solution without containing pyrochlore phase can be obtained when we consolidated the materials consisting of PbTiO3 and BaTiO3 at 1200℃ for 2 hours. The sintered body composed of 0.8Pb(Mg1/3Nb2/3)O3-0.1PbTiO3-0.1BaTiO3 composition showed the diffused phase transition(DPT) phenomena and the maximum value of dielectric constant at 0℃ (Tc') with the value of 1.3×104.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4347-4351
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• 2011

The nucleophilic substitution reactions of ethylene phosphorochloridate (2) with X-pyridines are investigated kinetically in acetonitrile at $-20.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. Unusual positive ${\rho}_X$ (= +2.49) and negative ${\beta}_X$ (= -0.41) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=6.6^{\circ}C$. The pyridinolysis rate of 2 with a cyclic five-membered ring is forty thousand times faster than its acyclic counterpart (3: diethyl chlorophosphate) because of great positive value of the entropy of activation of 2 (${\Delta}S^{\neq}$ = +49.2 eu) compared to negative value of 3 (${\Delta}S^{\neq}$ = -44.1 eu) over considerably unfavorable enthalpy of activation of 2 (${\Delta}H^{\neq}=28.4\;kcal\;mol^{-1}$) compared to 3 (${\Delta}H^{\neq}=6.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.623-627
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• 2016

$La_{1-x}Ba_xMnO_3$ (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature $T_C{\sim}342K$. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near $T_C$. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/kgK under a magnetic field change of 2.5T for the $La_{0.6}Ba_{0.4}MnO_3$ composition. The relative cooling power (RCP) is 79.31 J/kg for the same applied magnetic field.

• Progress in Superconductivity
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• v.1 no.2
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• pp.135-140
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• 2000

Distribution of Pr ions between Y- and Ba-site of the $Y(Ba_{1-Xn}Pr_{Xn})_2Cu_3O_y$ ($0{\leq}Xn{\leq}{0.3}$, Xn : nominal composition) material prepared by the solid state reaction method was studied. Although the samples have narrow superconducting transition, tiny peaks of $Y_2BaCuO_5$ impurity phase are included in the x-ray diffraction patterns suggesting that some of the Pr ions are entered into the Y-site. The distribution of Pr ions between Y- and Ba-site was determined by measuring the mass fraction of YBCO and $Y_2BaCuO_5$ phase for each sample through the Rietveld analysis of the x-ray diffraction data. About 60 % of Pr ions occupy the Y-site regardless of the Pr content. Various superconducting parameters such as the oxygen content and the hole concentration etc. are compared before and after the impurity correction.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.270-274
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• 2012

The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1c) with X-pyridines are investigated kinetically in acetonitrile at $-25.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 1c with a cyclic five-membered ring is $2.70{\times}10^5$ times faster than its acyclic counterpart (1a: phenyl ethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (${\Delta}S^{\neq}$ = +26 eu) compared to negative value of 1a (${\Delta}S^{\neq}$= -24 eu) over considerably unfavorable enthalpy of activation of 1c (${\Delta}H^{\neq}=20.5kcal\;mol^{-1}$) compared to 1a (${\Delta}H^{\neq}=12.7kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed on the basis of greater selectivity parameters (${\rho}_X$ = -1.99 and ${\beta}_X$ = 0.41) with the strongly basic pyridines compared to those (${\rho}_X$ = -0.42 and ${\beta}_X$ = 0.07) with the weakly basic pyridines.

• Bulletin of the Korean Chemical Society
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• v.31 no.11
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• pp.3279-3282
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• 2010

The reaction rates of 4-X-2,6-dinitrochlorobenzenes (X = $NO_2$, CN, $CF_3$) with Y-substituted benzylamines (Y = p-$OCH_3$, p-$CH_3$, H, p-Cl) in MeOH-MeCN mixtures were measured by conductometry at $25^{\circ}C$. It was observed that the rate constant increased in the order of X = $NO_2$ > CN > $CF_3$ and in the order of Y = p-$OCH_3$ > p-$CH_3$ > H > p-Cl. When the solvent composition was varied, the rate constant increased in the order of 100% MeOH < 50% (v/v) MeOH-MeCN < 100% MeCN. These results may be ascribed to the formation of hydrogen bonds between the alcoholic hydrogen and nitrogen of benzylamines in groud state (GS). We conclude that the reaction takes place via $S_NAr$ base on the transition state parameters ${\rho}x$, ${\rho}Y$, $\beta_{nuc}$, and solvent effects.

• Journal of the Korean Chemical Society
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• v.20 no.6
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• pp.453-459
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• 1976

Rate constants for the reaction of methyl chloroformate with substituted anilines, and for the halogen exchanges in phenyl chloroformate have been determined in acetone. Although the rate data can be interpreted equally well with the addition-elimination mechanism($S_AN$) involving an intermediate, results of MO and isotope effect studies strongly favor the synchronous ($S_N2$) mechanism for the reactions studied. It was concluded that for the fast reacting nucleophiles the transition state is of "late" type while for the slow reacting nucleophiles it is of "early" type.