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몰농도 또는 몰분율로 표시되는 임계 미셀 농도와 열역학적 포텐셜과의 관계
김홍운(Hong Un Kim),임경희(Kyung Hee Lim) 한국유화학회 2001 한국응용과학기술학회지 Vol.18 No.4
N/A The critical micelle concentration (CMC) at which micelles start to form from a surfactant solution is usually measured in terms of conventional concentration units. However, the thermodynamic potentials are expressed in terms of mole fraction X_CMC and X_CMC cannot be directly measured experimentally. The Gibbs free energy, △G^*_mic, in particular is related to X_CMC through △G^*_mic = RTln X_CMC. When it comes to CMC, the molar CMC, C_CMC, differs only by the proportionality C^-1_w with C_w being the molarity of water. Hence, C_CMC is found to be a proper representation of CMC. However, in calculation of △G^*_mic and other thermodynamic potentials from the CMC, X_CMC or C_CMC/C_w should be used.
유체역학과 분자 전이를 결합한 이론에 의한 다기포 음광 현상의 발광 기구 해석
김홍운 ( Hong Un Kim ),임경희 ( Kyung Hee Lim ),곽호영 ( Ho Young Kwak ) 한국공업화학회 2002 공업화학 Vol.13 No.7
다기포 음광(MBSL)이 발생되는 이유나 원인에 대하여 이제까지 확실하게 파악하지 못하고 있다. 단기포 음광을 설명하기 위하여 적용된 이론들 즉 흑체 복사와 제동 복사가 다기포성 음광을 설명할 수 있다고도 하였으나 다기포성 음광 스펙트라에서만 나타나는 강도(intensity) 피크에 의하여 이런 이론들이 유효하지 않다는 것이 밝혀지기도 하였다. 최근에 Suslick 등은 흑체 복사에 의한 연속 방사와 분자 전이에 의한 피크가 다기포성 음광 스펙트라를 설명할 수 있다고 발표하였으며, 입자의 크기가 직선적으로 줄어드는 단순한 모델에 대하여 이의 타당성을 보여주었다. 본 연구는 Suslick 등이 고찰한 이런 단순한 모델 대신에 기포의 실제 거동을 설명해 주는 기포 동역학을 이용하여 시간의 변화에 따른 온도, 압력, 기포의 반지름을 실제적인 상황에 잘 맞도록 구하고 이를 사용하여 화학전이에 의한 다기포 음광의 발광 기구를 규명해 보고자 하였다. 그 결과 화학종의 농도 분포는 대체로 Suslick 등의 결과와 비슷한 경향을 보였으며, 특히 OH의 피크 온도는 거의 일치하였다. 그러나, 분자 전이에 의한 발광 기구에 책임이 있는 여기된 OH 즉 OH^*의 피크는 관찰되지 않았다. 이는 아직도 다기포 음광의 발광 기구가 규명되지 못한 채 남아 있음을 의미한다. It has not been well understood why and how multibubble sonoluminescence (MBSL) takes place. In order to elucidate the mechanism of MBSL, some scholars have relied on the theories of black body and bremmstrahlung radiations, which have accounted for the single-bubble sonoluminescence. However, these theories are unable to explain why the peaks in intensity appears only in MBSL spectra (intensity vs. wavelength). Recently, Suslick et. al. hypothesized that the MBSL mechanism would be continuous by black body radiation and also of discrete peaks that reflected molecular transitions. They tried to prove their hypothesis with theoretical calculations for the bubble of which radius changed linearly with time. However, it has been known from theory and experiments that, in reality, the bubble radius varies nonlinearly. In this article, Suslick et al`s hypothesis on the MBSL mechanism has been examined for the Ar/water system with the combined hydrodynamics and molecular transition, but with nonlinearly varying bubble radius. It is found that the distribution of chemical species was similar to that by Suslick et al. and that the temperature at which the intensity peak located was identical to the reported value. However, the excited OH radical or OH^*, which is supposed to be responsible for the intensity peak, has been unobserved. This result implies that the MBSL mechanism proposed by Suslick et al. remains controversial.
Pulsed (Field) Gradient Spin Echo (PGSE) NMR에 의한 ADS/OTAC 혼합 수용액에서의 콜로이드 희합체의 자가 확산 계수
김홍운 ( Hong Un Kim ),임경희 ( Kyung Hee Lim ),김은희 ( Eun Hee Kim ),정재준 ( Chae Joon Cheong ) 한국유화학회 2002 한국응용과학기술학회지 Vol.19 No.4
N/A Transesterfication of vegetable oils and methanol with alkaline catalyst was carried out to produce biodiesel fuel by continuou process. The process consists of two static mixers, one tubular reactor and two coolers and gave 95∼99% of methyl ester yield from soybean oil and rapeseed oil. Experimental variables were the molar ration of methanol to vegetable oil, alkaline catalyst contents, flow rates, mixer element number. The optimum ranges of operating variables were as follows reaction temperature of 70℃, 1:6 of molar ratio of methanol to oil, 0.4%(w/w) sodium hydroxide based on oil, static mixer elements number of 24 and 4 min. residence time.
공업화학 촉매 / 반응공학 : Multibubble Sonoluminescence 를 이용한 Ni 촉매의 활성화
김홍운(Hong Un Kim),임경희(Kyung Hee Lim) 한국화학공학회 1999 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.37 No.6
This article deals with the activation of metal catalysts under MBSL environment and their performance tests through the hydrogenation of cyclohexene, octene, nonene, and decene to their corresponding alkanes. Natural Ni is well known to exhibit no catalytic activity for the hydrogenation reaction. However, when Ni powder of 3 ㎛ was treated under MBSL, it showed catalytic activity. When Ni catalyst was prepared in an ultrasonic field of 110 W, the hydrogenation reaction yields increased up to 18 % with decreasing molecular weight. When higher intensity of 193 W was used, this trend was unobserved. However, the yield for the hydrogenation of octene to octane was 45 %. This result implies that Ni catalysts formed under MBSL may replace more expensive Pt or Pd catalysts, leading to catalytic process innovations.
김홍운(Hong Un Kim),임경희(Kyung Hee Lim) 한국유화학회 2001 한국응용과학기술학회지 Vol.18 No.2
N/A Theoretical model has been studied for the transport phenomena of molecules in the system where an electric potential is applied to the system in the axial direction. The effect of electrophoretic convection in the polymeric media is significantly contributed to separate large ionic-molecules because the conformation of large ionic-molecule quickly orients in the field direction. The dependence of the transport in the polymeric media upon field intensity and molecular size aids in understanding the transport of large ionic-molecule in the system, since the convective velocity of large ionic-molecule is accelerated inside a porous material. The transport distance of individual large ionic-molecule can be predicted using the reptation theories.