Molecular Dynamic Study of a Polymeric Solution (I). Chain-Length Effect

Lee Young Seek,Ree Taikyue Korean Chemical Society 1982 Bulletin of the Korean Chemical Society Vol.3 No.2

Dynamic and equilibrium structures of a polymer chain immersed in solvent molecules have been investigated by a molecular dynamic method. The calculation employs the Lennard-Jones potential function to represent the interactions between two solvent molecules (SS) and between a constituent particle (monomer unit) of the polymer chain and a solvent molecule (CS) as well as between two non-nearest neighbor constituent particles of the polymer chain (CC), while the chemical bond for nearest neighbor constituent particles was chosen to follow a harmonic oscillator potential law. The correlation function for the SS, CS and CC pairs, the end-to-end distance square and the radius of gyration square were calculated by varying the chain length (= 5, 10, 15, 20). The computed end-to-end distance square and the radius of gyration square were found to be in a fairly good agreement with the corresponding results from the random-flight model. Unlike earlier works, the present simulation rsesult shows that the autocorrelation function of radius of gyration square decays slower than that of the end-to-end distance square.

Nano Pt Particles on TiO_2 and Their Effects on Photocatalytic Reactivity

Choi, Wonyong,Lee, Jaesang,Kim, Soonhyun,Hwang, Sangman,Lee, MyungChurl,Lee, TaiKyu 한국공업화학회 2003 Journal of Industrial and Engineering Chemistry Vol.9 No.1

The effects of nano-sized Pt deposits on TiO₂particles on the photocatalytic kinetics and mechanisms for the degradation of ammonia and trichloroacetate (TCA) in water and gaseous CO oxidation were investigated. Although platinization has been a routine method of TiO₂modification, its effects on photocatalytic reaction mechanisms in pollutant degradation need to be fully understood. TiO₂photocatalytic reactioThe effects of nano-sized Pt deposits on TiO₂particles on the photocatalytic kinetics and mechanisms for the degradation of ammonia and trichloroacetate (TCA) in water and gaseous CO oxidation were investigated. Although platinization has been a routine method of TiO₂modification, its effects on photocatalytic reaction mechanisms in pollutant degradation need to be fully understood. TiO₂photocatalytic reactions are usually non-selective mainly because of the strong oxidation potential of OH radicals. (1) By using TiO₂deposited with nano-Pt particles, we are able to oxidize MH₃selectively to N₂. While the pure TiO₂quantitatively transforms ammonia into nitrite and nitrate, Pt/TiO₂converts NH₃into N₂with reducing the total nitrogen concentration in the suspension. (2) TCA degrades photocatalytically in the presence or absence of dissolved O₂, which proposes that two mechanistic pathways (oxic vs. anoxic) are operative. While the anoxic path is not important on naked TiO₂, it becomes dominant on platinized TiO₂surface. Therefore, the introduction of dioxygen in aqueous suspension enhances the rate of TCA degradation on naked TiO₂but inhibits it on Pt/TiO₂. (3) Platinum deposition on TiO₂greatly enhances the photooxidation rate of CO and the degree of enhancement strongly depends on the kind of TiO₂substrate. Platinized Hombikat TiO₂shows the best activity. The photocatalytic conversion of CO to CO₂is quantitative in the presence of O₂and no CO₂is generated in the absence of O₂.

퍼스널 로봇을 위한 이기종 네트웍 운용 방안

추성호(Seongho Choo),Vitaly Li,이정배(Jungbae Lee),박태규(Taikyu Park),장익규(Ikgyu Jang),정기덕(Kideok Jung),최동희(Donghee Choi),박홍성(Hongseong Park) 대한전기학회 2004 정보 및 제어 심포지엄 논문집 Vol.2004 No.1

Molecular Theory of Superplastic Deformation

김창홍,이태규,Chang Hong Kim,Taikyue Lee Korean Chemical Society 1979 대한화학회지 Vol.23 No.4

소성변형에 대한 著者들의 이론을 초소성합금(Zn-Al eutectoid, A1-Cu, Pb-Sn, Sn-Bi, Mg-Al eutectics)에 적용하였다. 그 결과 초소성합금의 소성변형은 두 개의 grain boundary流動單位의 平行連結로 나타낼 수 있었다. 이 두 개의 流動單位는 流動式에 나타나는 parameter $X_{gj}/{\alpha}_{gj}$와 ${\beta}_{gj}$(j=1 혹온 2)로 表現할 수 있으며 이들을 實驗的으로 求할 수 있었다. 著者들의 流動式은 實驗과 잘 一致하였다. Strain rate sensitivity 對 -In(strain rate) 곡선을 이론으로 구한 결과 유동단위수만큼의 peak가 ${\beta}_{gj}$(j=1 or 2) 값에 따라 분리되어 나타났고 초소성의 조건도 ${beta}_{gj}$값에 의하여 결정됨을 알았다. ${\beta}_{gj}값의 粒子크기 依存性을 구하였고 온도변화에 따른 ${\beta}_{gj}$값 변화로부터 각 流動單位의 활성화엔탈피, ${\Delta}H_{gj}^{\neq}$도 구하였다. 그 결과 ${\Delta}H_{gj}^{\neq}$는 재료성분원소들의 grain boundary 자체확산에 의한 활성화엔탈피와 같이 나타났고 또 이들은 粒子 크기 증가에 마라 증가함을 보였다 The author's theory for plastic deformation was applied to superplastic alloys (Zn-Al eutectoid, Al-Cu, Pb-Sn, Sn-Bi, Mg-Al eutectics). The plastic deformation of the superplastic alloys could be described by two Maxwell models connected in parallel which represent two grain boundary flow units. The flow units are characterized by the two parameters $X_{gj}/{\alpha}_{gj}\;and\;{\beta}_{gj}$ (j=l or 2, g signifies the grain boundary) the values of which were obtained by applying our flow equation [Eq. (5)] to experiment. We confirmed that our flow equation describes the superplasticity very well. The curve of strain rate sensitivity m (=${\partial}\;In\;f/{\partial}\;In\;\dot{s})\;vs.\;-In\dot{s}$, where f and s are stress and strain rate, respectively, showed two peaks corresponding to flow unit gl and g2, the separation of the two peaks is determined by the difference between ${\beta}_{g1}\;and\;{\beta}_{g2}$. The condition of superplasticity is also determined by ${\beta}_{gj}$, which satisfies $\dot{s}_{mj}{\leqslant}1.53}{\beta}_{gj}$ [Eq.(13)], where $\dot{s}_{mj}$ is the s of the jth unit at the peak. The grain size dependence of ${\beta}_{gj}$ is described by $ln({\beta}_{gj})^{-1}$=alnx+b [Eq. (16)], where x is the grain size, and a and b are constants. The activation enthalpy for each flow unit, ${\Delta}H_{gj}^{\neq}$ was also determined from the temperature dependence of ${\beta}_{gj}$ which is proportional to the relaxation time of the j th unit. Since the superplasticity is determined by Eq. (13), and since ${\beta}_{gj}$ and ${\Delta}H_{gj}^{\neq}$ are related, we obtained the conclusion that superplasticity occurs in the system having small ${\Delta}H_{gj}^{\neq}$ values. The Aej values were equal to the activation enthalpies of grain boundary self-diffusion of the component atoms of the alloys, this accords with our proposed flow mechanism. The ${\Delta}H_{gj}^{\neq}$ value increases with grain size as expected from Eq. (16).

Theoretical Calculation of Activity Coefficients of Liquid Mixtures

문대원,전무식,이태규,Moon Dae-Won,Jhon Mu Shik,Lee Taikyue Korean Chemical Society 1977 대한화학회지 Vol.21 No.6

액체이론(Significant Structure Theory)를 단원자 분자로부터 다원자 분자에 이르는 여러 액체혼합물에 적용하여 전 농도 범위에서 액체 혼합물의 활동도 계수를 계산했다. 단원자 분자계(Ar-Kr, Kr-Xe)와 이원자 분자계$(Ar-O_2,\;N_2-CO)$와 메탄-크립톤계의 액체혼합물의 활동도 계수는 ${\delta}E_s$ 수정 변수에 의해 좋은 결과를 얻었다. 아르곤-질소, 산소-질소, 그리고 메탄-프로판계에 대해서는 이 외에 ${\delta}$V, ${\delta}$n 수정 변수가 더 필요했다. Significant structure theory was applied to some liquid mixture systems ranging from simple monatomic molecule systems to polyatomic molecule systems, and the activity coefficients ${\gamma}$ of the liquid mixture systems were calculated over whole mole fractions using the following thermodynamic relation $RTln_{{\gamma}i} = (\frac{{\partial A}^E}{{\partial N}_i})_{T,V,N_i} $ where $A^E$ represents the excess Helmholtz free energy, and $N_i$ is the number of molecules of component i. The activity coefficients of the solutions such as monatomic molecule systems (Ar-Kr, Kr-Xe) and diatomic molecule systems $(Ar-O_2,\;N_2-CO)$ and $CH_4-Kr$ systems whose components have similar shapes for intermolecular potential curves were calculated successfully only with the ${\delta}E_s$, correction parameter for energy $E_s$, for mixture systems. For other systems such as $Ar-N_2,\;O_2-N_2\;and\;CH_4-C_3H_8$ whose components have dissimilar intermolecular potential curve shapes an additional correction parameters ${\delta}$V and even one more parameter ${\delta}$n were necessary [see Eqs.(10)∼(12)].