• Macromolecular Research
• /
• 제11권5호
• /
• pp.311-316
• /
• 2003

The kinetics of photoinitiated polymerization of dimethacrylate macromonomers have been studied to determine the diffusion-controlled reaction parameters using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). A predicted kinetic rate expression with a diffusion control factor was employed to estimate an effective rate constant and to define the reaction-controlled and diffusion-controlled regimes in the photopolymerization. An effective rate constant, k$_{e}$, can be obtained from the predicted kinetic rate expression. At the earlier stages of polymerization, the average values of kinetic rate constants do not vary during the reaction time. As the reaction conversion, $\alpha$, reaches the critical conversion, $\alpha$$_{c}$, in the predicted kinetic expression, the reaction becomes to be controlled by diffusion due to the restricted mobility of dimethacrylate macromonomers. A drop in value of effective rate constant causes a drastic decrease of reaction rate at the later stages of polymerization. By determining the effective rate constants, the reaction-controlled and diffusion-controlled regimes were properly defined even in the photopolymerization reaction system.m.m.

• Bulletin of the Korean Chemical Society
• /
• 제27권8호
• /
• pp.1181-1185
• /
• 2006

By using two different computer simulation methods, of which one produces exact results while the other is based on the Wilemski-Fixman closure approximation, we evaluate the utility of closure approximation in calculating the rates of diffusion-controlled reactions involving a reactant with multiple reaction sites. We find that errors in the estimates of steady-state rate constants due to closure approximation are not so large. We thus propose an approximate analytic expression for the rate constant based on the closure approximation.

• 폴리머
• /
• 제27권5호
• /
• pp.421-428
• /
• 2003

반응성 올리고머 및 메타아크릴레이트/SBS블렌드의 확산에 의해 제어되는 광중합 반응 특성을 ATR-FTR을 이용하여 고찰하였다. 광중합 속도는 반응 초기 단계에서는 자가 가속 현상을 보이며 반응 속도가 급격하게 증가하여 반응이 진행함에 따라 확산에 의한 반응 지연 현상이 관찰된다. 확산 제어항이 도입된 반응 기구 속도식으로 반응 속도를 해석한 결과 전체 반응 구간에서 실험 결과와 잘 일치하였다. SBS의 도입을 위해 사용된 반응성 용매인 N-비닐피롤리돈 (NVP)의 첨가에 의해서 최종 전환율에 이르는 시간은 거의 일정하였으나 전환율은 NVP의 높은 반응성으로 인하여 증가하는 경향을 보였다. 중합 반응 속도도 NVP 첨가에 의하여 증가하는 경향을 보였다. SBS의 첨가시 NVP-SBS의 함량이 10 phr까지는 동일한 전환율 거동을 보이나 NVP-SBS의 함량이 20 phr에서는 현저히 떨어지게 되는데 이는 NVP-SBS의 함량이 20 phr에서는 블렌드의 점도가 증가하여 반응에 영향을 주는 것으로 보인다. NVP-SBS의 함량이 증가함에 따라 중합 반응 속도는 점진적으로 감소함을 알 수 있었다. 메타아크릴레이트./SBS의 블렌드는 상온과 여러 높은 온도 범위에서 상분리가 관찰되지 않았으며 광중합 반응 후에도 투명한 준-IPN을 형성하여 성공적으로 필름 및 코팅에 적용할 수 있었다.

• 한국세라믹학회지
• /
• 제33권6호
• /
• pp.718-724
• /
• 1996

Deformation mechanism map of Langdon-Mohammed type for YBa2Cu3O7-x superconducting ceramic was constructed by considering mechanisms of Nabarro-Herring Coble and powder-law creep and grain boundary sliding (GBS) with an accommodation by grain boundary diffusion. The map was found consistent with experi-mental results not only of the creep the also of the superplastic deformation. It showed the transition from interface reaction-controlled to the grain boundary diffusion-controlled GBS mechanism at about 1 ${\mu}{\textrm}{m}$ grain size and 100 MPa flow stress in agreement with the experimental results.

• 공학논문집
• /
• 제3권1호
• /
• pp.223-233
• /
• 1998

고상반응식을 이용한 석회와 석영과의 수열반응속도 및 반응메카니즘에 관하여 연구하였다. 출발물질로 석영과 수산화칼슘 CaO/$SiO_2$몰비 0.8-1.0로 혼합하고 $180-200^{\circ}C$, 0.5-8시간동안 포화증기압하에서 오토클레이브로 수열반응을 행하였다. 수열반응속도는 총 석회의 양과 총 석영의 양에 대한 미반응 석회의 양과 미반응 석영의 양의 비로 구하였다. 반응속도는 Jander의 식 $[1-(1-\alpha)^{1/3}]^N=Kt$를 이용하여 얻은 결과, 석회의 반응속도는 N=1로서 주로 용해속도에 의해 지배되고 석영의 반응속도는 $N\risingdotseq2$로서 확산에 의해 주로 지배된다. 규산칼슘수화물계의 수열반응속도는 반응물 입자주위에 형성된 생성물층을 통한 물질전달에 의해 율속되는 것으로 추정되고 전체 수열반응의 속도식은 대략 $N=1-2$로서 경계층으로부터 확산에 의해 율속과정으로 전환된다.

• Bulletin of the Korean Chemical Society
• /
• 제32권spc8호
• /
• pp.2973-2977
• /
• 2011

It has been known that the inertial dynamics has a little effect on the reaction rate in solutions. In this work, however, we find that for diffusion-controlled reactions between a ligand and a receptor on the cell surface there is a noticeable inertial dynamic effect on the reaction rate. We estimate the magnitude of the inertial dynamic effect by comparing the approximate analytic results obtained with and without the inertial dynamic effect included. The magnitude of the inertial dynamic effect depends on the friction coefficient of the ligand as well as on the relative scale of the receptor size to the distance traveled by the ligand during its velocity relaxation time.

• 폴리머
• /
• 제24권1호
• /
• pp.105-112
• /
• 2000

본 연구에서는 항공기 구조용 재료로 쓰이는 탄소섬유/에폭시 복합재료 프리프레그(DMS 2224)를 모델시스템으로 하여 등온환경과 등속도 가열환경에서 경화반응 속도를 연구하였다. 이 복합재료의 공정온도에서의 가공공정을 묘사할 수 있는 현상학적인 반응속도 모델을 differential scanning calorimetry (DSC)와 이론을 통하여 제안하였다. 등온환경에서의 실험으로부터 반응특성곡선을 관찰한 결과 경화반응이 1차 반응함수임을 확인하였고, 활성화 에너지는 78.43 kJ/mo1을 얻었다. 이 프리프레그는 경화온도에 따라 한계경화도를 보여주어 유리화가 존재함을 확인하였고 이를 1차 반응속도 모델에 적용시킨 결과, 유리화 이후의 확산우세현상을 포함한 반응속도 모델을 제안하였다. 제안된 모델식을 이용하여 등온/등속도 가열환경을 포함한 실제 경화공정을 성공적으로 표현할 수 있었다.

• Journal of Welding and Joining
• /
• 제15권3호
• /
• pp.128-135
• /
• 1997

Reaction diffusion and formation of $Ni_3Al$phase with $L1_2$ structure have been studied in temperature range of 1432K to 1573K using the diffusion couple of (Ni-40, 5at%Al)/(Ni-14, 1at%Al) and (Ni-49, 2at%Al)/ (Nickel). The layer growth of Ni$_{3}$Al pyhase in the annealed diffusion couple was measured by optical microscope and electron probe microanalyzer (EPMA). The layer growth of $Ni_3Al$phase in diffusion zone obeyed the parabolic law without any indication of grain boundary effects. The layer growth of $Ni_3Al$phase in temperature range of 1423K to 1573K was mainly controlled by the volume diffusion mechanism. The rate of layer growth of $Ni_3Al$phase was found to be colsely related to the composition of intermetallic compound NiAl phase. The activation energy for layer growth of $Ni_3Al$phase was calculated to be 127kJ/mol.

• Macromolecular Research
• /
• 제10권5호
• /
• pp.259-265
• /
• 2002

The cure kinetics of blends of epoxy (DGEBA, diglycidyl ether of bisphenol A)/anhydride resin with polyamide copolymer, poly(dimmer acid-co-alkyl polyamine), were studied using differential scanning calorimetry (DSC) under isothermal condition. On increasing the amount of polyamide copolymer in the blends, the reaction rate was increased and the final cure conversion was decreased. Lower values of final cure conversions in the epoxy/(polyamide copolymer) blends indicate that polyamide hinders the cure reaction between the epoxy and the curing agent. The value of the reaction order, m, for the initial autocatalytic reaction was not affected by blending polyamide copolymer with epoxy resin, and the value was approximately 1.3, whereas the reaction order, n, for the general n-th order of reaction was increased by increasing the amount of polyamide copolymer in the blends, and the value increased from 1.6 to 4.0. A diffusion-controlled reaction was observed as the cure conversion increased and the rate equation was successfully analyzed by incorporating the diffusion control term for the epoxy/anhydride/(polyamide copolymer) blends. Complete miscibility was observed in the uncured blends of epoxy/(polyamide copolymer) up to 120 $^{\circ}C$, but phase separations occurred in the early stages of the curing process at higher temperatures than 120 "C. During the curing process, the cure reaction involving the functional group in polyamide copolymer was detected on a DSC thermogram.gram.

• 한국마이크로전자및패키징학회:학술대회논문집
• /
• 한국마이크로전자및패키징학회 2001년도 추계 기술심포지움
• /
• pp.134-137
• /
• 2001

The cure kinetics of a cycloalipatic epoxy / anhydride / Co(II) system for a no-flow underfill encapsulant, has been studied by using a differential scanning calorimetry(DSC) under isothermal and dynamic conditions over the temperature range of $160^{\circ}C ~220^{\circ}C$. The kinetic analysis was carried out by fitting dynamic/isothermal heating experimental data to the kinetic expressions to determine the reaction parameters, such as order of reaction and reaction constants. Diffusion-controlled reaction has been observed as the cure conversion increases and successfully analyzed by incorporating the diffusion control term into the rate equation. The prediction of reaction rates by the model equation corresponded well to experimental data at all temperature.