Reaction kinetics and interfacial properties in reactive polymer blends : a Monte Carlo study = 몬테칼로 기법을 이용한 반응성 고분자 블렌드의 반응동역학과 계면물성에 관한 연구

양유성 서울대학교 대학원 2004 국내박사

섞이지 않는 고분자 블렌드에 반응기를 가진 반응성 고분자를 투입하였을 때 반응성 고분자간의 계면에서 반응을 할 때 반응기의 개수와 농도가 반응 동역학과 계면물성에 어떤 영향을 미치는지 몬테칼로기법을 이용하여 연구하였다. 우선 반응기가 한쪽끝에만 있는 mono-endfunctional 고분자와 di-endfunctional 고분자를 이용하여 시뮬레이션을 수행하였을 때, 반응 초기에 반응양이 급격히 증가하다 일정한 값으로 수렴하게 됨을 알 수 있었다. 반응성 고분자의 농도가 낮은 경우에 mono-endfunctional reaction system (MERS)와 di-endfunctional reaction system (DERS) 모두 수렴하는 값이 농도에 비례하였으나 DERS의 경우 농도가 한계점을 넘어서면서 반응성 고분자의 농도에 비례하지 않음을 확인하였다. 이는 di-endfunctional 고분자가 반응을 통해서 만들어 내는 공중합체의 구조에 기인하는 것이며 반응기의 양쪽이 모두 반응한 loop 형태가 감소를 하게 되고 이와 반대로 한쪽 끝만 반응한 tail 형태와 반응을 하지 않은 양이 급격하게 늘어남에 따라 이러한 거동을 보이게 된 것이라고 알 수 있었다. 실험적인 결과와 비교하기 위해 계면에서의 fracture toghness값과 비교하였을 때 이 실험값과 반응하여 만들어진 공중합체의 양이 동일한 형태를 보이고 있어서 시뮬레이션의 신빙성을 높일 수 있었다. 이와 동시에 중요한 계면물성중의 하나인 계면두께와 계면장력을 계산하였는데 이 두가지 물성또한 농도에 영향을 받아 농도가 상대적으로 낮은 경우는 각각 증가하고 감소하다가 한계농도에 이르게 되면 일정한 값으로 수렴하게 됨을 알 수 있었다. 또한 계면장력의 경우 이론적인 계산으로 비교를 해보았는데 이론적으로는 계면에서 공중합체의 구조를 고려하지 않았기 때문에 계면장력이 계속해서 값이 떨어지는 값을 보여 시뮬레이션과 다른 결과를 보였다. 실험적으로 보면 어느정도 값이 떨어지다 일정해지는 것이 잘 알려진 사실이기 때문에 계면물성 연구에는 시뮬레이션이 훨씬 더 정확도를 가지고 있다고 할 수 있다. 두번째로 고분자 말단에 반응기를 넣는 것 뿐만 아니라 가운데 부분에도 추가하여 tri-functional 고분자를 만들었을 때 반응동역학과 반응으로 생긴 공중합체의 구조를 파악하였다. 시뮬레이션 상자내부에 들어 있는 A 반응성 고분자 부분과 B 반응성 고분자 부분에 있는 반응기의 개수가 다른 nonstoichiometric 시스템과 개수가 동일한 stoichiometric 시스템으로 나눠서 비교를 했을 경우, 실제로 시뮬레이션에서 가운데 부분에 있는 반응기는 엔트로피가 낮기 때문에 반응에 참여하는 빈도가 매우 낮고 결국 반응 속도를 높이는데 효과적이지 못하다. 엔트로피 효과로 인해 양쪽에 있는 반응기가 반응에 많이 참여하게 되고 loop나 tail형태의 비율이 상당히 많아진다. Nonstoichiometry 시스템에서는 반응기의 개수가 많은 tri-functional 고분자가 반응에 모두 참여하지 못하고 반대로 tri-functional 고분자와 반응을 하는 mono-endfunctional 고분자와 di-endfunctional 고분자가 반응을 지배하는 반응 메커니즘을 따르게 된다. 위 내용을 고려해볼 때 반응동역학과 반응을 통해 형성된 공중합체의 구조를 결정하는데 있어 고분자내의 반응기의 위치가 매우 중요하다는 것을 알게 되었다. Monte Carlo (MC) simulation was used to investigate the effects of reactive polymers with functional groups on a chain on the reaction kinetics and interfacial properties of an A/B immiscible polymer blend. First, we studied reactions at the interface of two immiscible polymers containing different reactive groups at either one end or both ends are studied with MC simulations. The MC simulation shows that the copolymer concentration at the interface is shown to dramatically increase during the early stage of reaction and then levels off at a constant value. The effect of endfunctionality, i.e., the effect of the number of endfunctional groups, is also investigated. While the saturation value of interfacial coverage is proportional to the initial reactive polymer density for the case of mono-endfunctional polymer, the simulation results with di-endfunctional polymers show that the saturation copolymer coverage is not exactly proportional to the initial reactive polymer density in the case of high concentrations of the initial reactive polymer. This is believed to be because of the change of conformation of block copolymers formed at the interface due to reaction: the fraction of loop conformation decreases while the tail fraction increases with a large amount of initial reactive di-endfunctional polymer. Also, the experimentally determined time-dependent interfacial fracture toughness, which is, in turn, related to the copolymer coverage at the interface, is in good qualitative agreement with the simulation results. We also studied effects of endfunctionality and concentration of reactive polymers on interfacial thickness and interfacial tension. Interfacial thickness is increased up to and interfacial tension is decreased down to practical limits respectively at the threshold concentration of reactive polymer due to the sudden change in the conformation of copolymers at the interface: the fraction of loop conformation decreases, but the conformation fractions of tail and unreacted di-endfunctional polymer are increased after the threshold concentration of reactive polymer. We compare the simulation result of the interfacial tension with the theoretical calculation of the interfacial tension and find out that the simulation result is more adequate for prediction of the actual interfacial tension. All the results in the simulation are strongly consistent with one another. Second, we investigated the effect of functionality of reactive polymers on the reaction kinetics and chain conformation formed at the interface due to reaction. The position of reactive groups as well as the number of reactive groups along a chain significantly determines the reaction kinetics and chain conformation both in a stoichiometric system in which the number of A reactive polymers is the same as of B reactive polymers and in a nonstoichimetic system in which the number of A reactive polymers is different from that of B reactive polymers. The reactive site of the central position on a tri-functional polymer are not effective in enhancing the reaction rate and the fraction of copolymer made by participation of the central reactive group in the reaction is very small due to low degree of freedom of central position along a chain. Chain ends of a reactive polymer are much more preferred for the reaction at the interface due to entropic effect. In a nonstoichiometric system, reactive polymers with fewer reactive groups, mono-endfunctional polymers or di-endfunctional polymers control the reaction rate in mono-endfunctional/tri-functional reaction system and di-endfunctional/tri-functional reaction system, respectively. This means that the topological effect of reactive groups along a chain is an important factor in determining the reaction rate and copolymer conformation.

Reaction Acceleration at Interfaces Studied by Mass Spectrometry

Li, Yangjie Purdue University ProQuest Dissertations & Theses 2021 해외박사(DDOD)

Various organic reactions, including important synthetic reactions involving C-C, C-N, and C-O bond formation as well as reactions of biomolecules, are known to be accelerated when the reagents are present in confined volumes such as sprayed or levitated microdroplets or thin films. This phenomenon of reaction acceleration and the key role of interfaces played in it are of intrinsic interest and potentially of practical value as a simple, rapid method of performing small-scale synthesis. This dissertation has three focusing subtopics in the field of reaction acceleration: (1) application of reaction acceleration in levitated droplets and mass spectrometry to accelerate the reaction-analysis workflow of forced degradation of pharmaceuticals at small scale; (2) fundamental understanding of mechanisms of accelerated reactions at air/solution interfaces; (3) discovery the use of glass particles as a 'green' heterogeneous catalysts in solutions and systematical study of solid(glass)/solution interfacial reaction acceleration as a superbase for synthesis and degradation using high-throughput screening.Reaction acceleration in confined volumes could enhance analytical methods in industrial chemistry. Forced degradation is critical to probe the stabilities and chemical reactivities of therapeutics. Typically performed in bulk followed by LC-MS analysis, this traditional workflow of reaction/analysis sequence usually requires several days to form and measure desirable amount of degradants. I developed a new method to study chemical degradation in a shorter time frame in order to speed up both drug discovery and the drug development process. Using the Leidenfrost effect, I was able to study, over the course of seconds, degradation in levitated microdroplets over a metal dice. This two-minute reaction/analysis workflow allows major degradation pathways of both small molecules and therapeutic peptides to be studied. The reactions studied include deamidation, disulfide bond cleavage, ether cleavage, dehydration, hydrolysis, and oxidation. The method uses microdroplets as nano-reactors and only require a minimal amount of therapeutics per stress condition and the desirable amount of degradant can be readily generated in seconds by adjusting the droplet levitation time, which is highly advantageous both in the discovery and development phase. Built on my research, microdroplets can potentially be applied in therapeutics discovery and development to rapidly screen stability of therapeutics and to screen the effects of excipients in enhancing formulation stabilities.My research also advanced the fundamental understanding of reaction acceleration by disentangles the factors controlling reaction rates in microdroplet reactions using constantvolume levitated droplets and Katritzky transamination as a model. The large surfaceto-volume ratios of these systems results in a major contribution from reactions at the air/solution interface where reaction rates are increased. Systems with higher surface-active reactants are subject to greater acceleration, particularly at lower concentrations and higher surface-to-volume ratios. These results highlight the key role that air/solution air/solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction increased rate constant is at least in part due to limited solvation of reagents at the interface.While reaction acceleration at air/solution interfaces has been well known in microdroplets, reaction acceleration at solid/solution interfaces appears to be a new phenomenon. The Katritzky reaction in bulk solution at room temperature is accelerated significantly by the surface of a glass container compared to a plastic container. Remarkably, the reaction rate is increased by more than two orders of magnitude upon the addition of glass particles with the rate increasing linearly with increasing amounts of glass. A similar phenomenon is observed when glass particles are added to levitated droplets, where large acceleration factors are seen. Evidence shows that glass acts as a 'green' heterogeneous catalyst: it participates as a base in the deprotonation step and is recovered unchanged from the reaction mixture.Subsequent to this study, we have systematically explored the solid/solution interfacial acceleration phenomena using our latest generation of a high-throughput screening system which is capable of screening thousands of organic reactions in a single day. Using desorption electrospray ionization mass spectrometry (DESI-MS) for automated analysis, we have found that glass promotes not only organic reactions without organic catalysts but also reactions of biomolecules without enzymes. Such reactions include Knoevenagel condensation, imine formation, elimination of hydrogen halide, ester hydrolysis and/or transesterification of acetylcholine and phospholipids, as well as oxidation of glutathione. Glass has been used as a general 'green' and powerful heterogeneous catalyst.

Reaction Dynamics of Atomic Chlorine with Vibrationally Excited Methane : Oriented Photofragments in Molecular Photodissociation

김지환 Stanford University 2002 해외박사

Part I of this thesis presents the investigation of the reaction of atomic chlorine (Cl^(2)P_(3/2)) with the vibrationally excited methane (CH₄), using the photo-initiated reaction technique. A mixture of the Cl₂, CH₄and He is supersonically expanded into a vacuum chamber, and the CH₄reagent is vibrationally excited by a resonant IR radiation. The reaction is initiated by the photodissociation of the Cl₂and the reaction products (HCl and CH₃) are state-selectively detected by 2+1 resonanceenhanced multiphoton ionization (REMPI) in a Wiley-McLaren time-of-flight (TOF) spectrometer. The product state distributions, spatial anisotropies and the stateresolved differential cross sections are measured. The main focus of this work is on understanding of the effects of the different modes of vibrational excitation of methane on reaction dynamics. It is found that the stretch-excitation of C-H bond leads exclusively to H-atom abstraction for partially deuterated methanes. In addition, two different modes of stretch-overtone excitation of methane (|11〉:one quantum in each of two different C-H stretches,|20〉:two quanta in one C-H stretch) leads to different vibrational states of the methyl radical product. These observations indicate that the H-atom abstraction reaction proceeds as if the rest of the methane molecule plays only the role of spectator. The energy disposal and angular distributions for the reaction Cl + CH₄(|1100;F₂〉) (one quantum each in two of the four C-H bonds;|11〉) are also studied in detail. Spatial anisotropies of HCl and CH₃products allow identification of three major product channels. They are in order of importance: (a) HCl (v = 0) + CH₃[ν₁(symmetric stretch) or ν₃(asymmetric stretch)=1]; (b) HCl (v=1) + CH₃[ν₂(umbrella bend)=1)]; and (c) HCl (v=1) + CH₃(ν₁=1). The CH₃(v=0) product cannot be detected, and the HCl (v=2) product is minor. Channels (a) and (c) proceed in a vibrationally adiabatic manner, whereas channel (b) appears to involve the nonadiabatic interaction involving the low frequency bending mode in methane that correlates to the bending mode in the methyl radical product. The angular distributions differ markedly for the three product channels. This behavior is explained by the propensity for reactive collisions involving H-atom transfer along the line of centers and the difference in the cones of acceptance. The rotational angular momentum vector of the HCl (v = 1, J = 1) product is aligned perpendicular to the line of centers, which is consistent with an impulsive energy release along the line of centers. The dynamics of the Cl + CHD₃|2000;A1〉reaction is compared to the dynamics of the Cl + CH₄|1100; F2〉reaction. The observation of a substantial amount of HCl (v=2) product from the|20〉-mode enhanced reaction provided us with the complementary evidence of the direct and localized nature of the C-H stretch excited reaction. The angular distributions and the rotational distributions of HCl products indicate that the HCl (v=2) product channel has a restricted cone-of-acceptance for the reaction, whereas the HCl (v=1) channel has a substantially wider cone of acceptance. The reaction of Cl atoms with CH₄(ν2 +ν4) is studied in order to understand the role of bending-mode excitation. We have established that this reaction is at least 10 % as reactive as the ν₃-driven reaction. We find no pronounced propensity for the formation of CH₃(ν₂= 1), in contrast to the theoretical predictions from the adiabatic correlation of the vibrational modes of the CH₄and CH₃. The HCl(v=0) products show broad side and backward scattering. Both of the HCl and the CH₃ products show substantial rotational excitations. It is believed that the product rotational excitation is caused by the tangential motion of C-H bond mapped onto the rotational motion of the products. Relative reactivities of the ground [Cl(^(2)P_(3/2))] versus spin-orbit excited state Clatom [Cl^(*)(^(2)P_(1/2))] with the CH₄(v=0) is studied using the BrCl molecule as a precursor for the Cl and Cl^(*). Measured spatial anisotropy of the CH₃product indicates the Cl^(*) + CH₄reaction channel is unimportant in the near-threshold collision energy range of 0.13 - 0.16 eV, whereas the reaction with ground-state Cl atoms with CH₄excited with one quantum in the ν₂(torsion) or ν₄(bending) mode is dominant. Part II of this thesis presents the study of the oriented photofragments in the photodissociation of simple molecules. Electronic orbital orientation of the atomic photofragments is caused by the quantum mechanical coherence between the two pathways that originate from a mixed parallel and the perpendicular transition. An extended formalism is developed for the photofragments (atomic and diatomic) from the photodissociation of bent triatomic molecules. We show that the the broken symmetry associated with a bent triatomic molecule causes both coherent and incoherent orientation of the photofragments. Orientation moments of the Cl^(*)(^(2)P_(1/2))-atom photofragments from the photodissociation of the molecular chlorine (Cl₂) are studied in the wavelength range 270-400 nm, with linearly polarized light. The orientation of the excited-state chlorine atom Cl^(*)(^(2)P_(1/2)) is probed by 2 + 1 resonance enhanced multiphoton ionization (REMPI) using circularly polarized light. The degree of orientation of the Cl^(*) photofragment is found to oscillate as a function of photolysis wavelength. The measured orientation is caused by the interference between the adiabatic pathway of the B³Ⅱ(□)-X¹∑(□) transition and the nonadiabatic pathways that involve the C¹Ⅱ(□)-X¹∑(□)transition followed by the nonadiabatic radial-derivative coupling to other excited states with Ω= 1_(u) symmetry. Orientation moments of the S (^(1)D_(2)) and CO (X¹∑^(+)) from the photodissociation of carbonyl sulfide (OCS) are studied at 223 nm, with linearly polarized light. Orientation moments of the S(^(1)D_(2)) and co(X¹∑^(+)) are probed by (2 + 1) resonance enhanced multiphoton ionization (REMPI) using circularly polarized light. Fast S atoms show a large orientation, whereas slow S atoms show little or no orientation. Orientation of S-atom results from quantum mechanical coherence associated with mixed parallel ^(1)A´(^(1)△)-^(1)A´(^(1)∑^(+)) and perpendicular ^(1)A˝(^(1)∑^(-))-^(1)A´(^(1)∑^(+)) transitions that lead to the same photofragment state S(^(1)D_(2)). Comparison of the speed-dependent orientation with the expected envelope of the oscillation of the orientation suggests that the asymptotic phase differences of the two wave functions are nearly constant over different rotational states of the CO photofragment. This result can be explained by the similarity of the two potential energy surfaces involved. Measured orientation of the CO photofragments oscillates between clockwise and counter-clockwise directions as a function of the rotational quantum number of CO. In addition, use of circularly polarized photolysis induces a lab-frame A_(0)^((1)) 0 moment, which cannot be explained by a simple recoil picture for the photodissociations. Three different mechanisms are proposed to explain the observed trends in the orientation of CO photofragments.

Reaction mechanism study on the atomic layer deposition of silicon nitride : 실리콘 질화막의 원자층증착 반응기구 연구

박재민 세종대학교 대학원 2017 국내박사

Over the past 50 years, the semiconductor devices have been densified by two-dimensional (2D) scaling, and their performance have been improved by applying new materials such as Cu interconnect, low-k, SiGe, high-k and metal gates. Recently, new three-dimensional (3D) structures has begun to be adopted. For logic devices, 2D planar transistors are converted to 3D structured FinFETs, and even for NAND flash memory devices, memory cells that have been horizontally integrated are being replaced by memory cells with 3D structures stacked with dozens of vertical layers. Atomic layer deposition (ALD) is gaining attention as the most promising candidate to replace existing thin film deposition technologies such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. Since ALD is an atomic layer-by-layer growth process based on self-limiting surface reactions, this technique can produce uniform and conformal thin films on complex 3D structures with very high aspect ratios at low temperatures. Silicon nitride thin film has been widely used because of their chemical stability and resistance to diffusion of impurities as well as their etching selectivity compared to SiO2 and Si. The most important applications of silicon nitride films in next-generation semiconductor devices include the gate spacers in field-effect transistors and the charge trap layers in NAND flash devices. Various precursors and reactants have been studied for the ALD of silicon nitride films for these applications, and there is a growing interest in the reaction mechanism of the ALD of silicon nitride. Understanding the deposition reaction mechanism of ALD is very important because it affects the composition, structure and the properties of the deposited films. In order to grow silicon nitride films with an excellent step coverage and high quality, this dissertation focuses on predicting the surface chemical reactions by density functional theory (DFT) calculations and on identifying the ALD reaction mechanism by in-situ monitoring techniques The energies of surface reactions for the 1st half reaction of ALD process, such as adsorption energy, reaction barrier and reaction energy, were calculated by DFT. The bond dissociation energy (BDE), the highest occupied molecular orbit (HOMO), the lowest unoccupied molecular orbit (LUMO) and charge density were also calculated to predict the characteristics of precursors and substrates. The substrate was modeled as two types: NH*/NH2*-terminated β-Si3N4 surface and under-coordinated β-Si3N4 surface. The reaction was monitored by measuring the weight change of the growing film using the quartz crystal microbalance (QCM) and analyzing the chemical species on the pellet surface using Fourier transform infrared (FTIR) spectroscopy. Thermal ALD SiN was investigated using chloride precursor. The DFT calculation was used for analyzing the BDE and reaction pathways to understand the reaction mechanism. The various reaction paths of Si3Cl8 were calculated and then compared with the in-situ monitoring results and experimental results. Increasing the number of silicon atoms in precursor, the BDE values of Si–Si was weaker from 3.52 eV to 3.33 eV and the BDE values of Si–Cl also weaker from 4.62 eV to 4.35 eV. Among silicon chlorides, Si3Cl8 showed the fastest reaction with the lowest BDE value, which is related in 1st half reaction. The saturation dose was reduced from 1010 L to 107 L and the deposition temperature was decreased to 300℃ with a high growth rate of ~0.2 nm/cycle. However, Si3Cl8 shows different growth kinetics at different deposition temperatures. The adsorption at high temperature is expected to make –SiCl2 species and the formation of 2HSiCl3 by-products after the 1st half reaction. On the other hands, two Si-N bonds generated with the low energy barrier of 1.38 eV, and the deposited film showed Si-rich concentration at low temperature. Because it is difficult to remove –Cl after silicon chloride precursors are adsorbed on the substrate. Therefore, it is necessary to use NH3 and NH3 plasma at a high temperature or to use a stronger nitriding agent. The PEALD process was studied using aminosilane precursors to grow high quality silicon nitride films at low temperatures. To simulate the PEALD process, under-coordinated silicon nitride surface formed by N2 plasma was modeled. The new precursor was designed to improve film quality, based on TSA. To improve the thermal stability, reactivity and vapor pressure of the precursors, the –SiH3 ligand was substituted with the –SiMe3 ligand and the –(MeSiHNMe2) ligand and then the precursor properties were compared using the DFT calculation. The 1st half reaction was calculated on the under-coordinated silicon nitride surface after selecting bis (dimethylaminomethylsilyl) trimethylsilyl amine (DTDN2-H2) among several TSA derivatives. The reaction energy barrier of DTDN2-H2 was ~1.5 eV. As a low energy barrier, DTDN2-H2 had a wide ALD window from 250℃ to 400℃ and GPC was 0.36 Å/cycle. It showed excellent step coverage of more than 80% in trench structure with AR of 5. Since the silicon nitride films for next-generation semiconductor devices required a better step coverage, a new precursor was designed that are superior to the TSA derivatives. To increase the thermal stability and reactivity of the precursors, a ring structure of Si-N bonds was designed and a suitable ligand was added to have sufficient vapor pressure for the ALD process. The energy of barrier of the designed 1,3-di-isopropylamino-2,4-dimethylcyclosilazane (CSN-2) was 1.32 eV, which is lower than that of DTDN2-H2 in the 1st half reaction. And CSN-2 showed a wider ALD window from 200℃ to 500℃ with GPC of 0.43 Å/cycle. All of the deposited films in the ALD window region showed excellent step coverage over 90%. However, WER properties of the films deposited on the bottom sidewall at low temperature were not good. This is a limitation caused by plasma recombination loss of the N radical. In order to solve this problem, a new 3-step PEALD process was designed by adding NH3/N2 plasma to the standard N2 plasma PEALD process. The NH3 plasma can more effectively remove the ligands of the adsorbed precursor, but it is difficult to adsorb the precursor in the next cycle by forming NH*/NH2* surface. The following N2 plasma treatment removes –H on the surface and activates the surface so that the precursor is easily adsorbed in the 1st half reaction. As a result, silicon nitride films having high quality and excellent step coverage were deposited on a trench with high aspect ratio. The bottom sidewall coverage was improved from 81% to 95% and the wet-etch characteristic was improved form 13 Å/min to 3 Å/min. In this dissertation, the in-situ process monitoring and DFT calculations successfully applied to explain the ALD reaction mechanism for growth of silicon nitride films with excellent film quality. And the precursors are designed by calculation of the precursor properties, and the calculation results well predicts the experimental results.

Study on the mechanisms of photo- and electro-catalytic system for water splitting reaction

박승학 서울대학교 대학원 2019 국내박사

Developing the suitable catalyst system for desired reaction is one of the most important goal of research community that has great significance both industrially and scientifically. In particular, catalytic systems that convert solar energy to hydrogen fuel by photo-/electro-chemical water splitting, have been attracting much attention recently as being an ideal technology for solving the environmental and energy problems of mankind and achieving a sustainable future energy system. As a result of many previous researches, the efficiency of catalyst system has been continuously improved stand on the descriptor based volcano approach that is supported by various experimental and calculation results. Although the catalyst system design guided by the descriptor based volcano approach has leaded to achieve an integrated understanding of the system and increase the efficiency continuously, a new system design approach is needed to break the volcano limitation of previous approach and to attain the practically economic efficiency of the catalyst system. In this regard, detailed understanding the reaction mechanism of the efficient catalyst system is essential to be the basis for the rational design of the improved catalyst system. In general, the catalytic reaction cycle is not a simple single-step but a complex multi-step involving activation, substrate binding, product liberation, and regeneration process. Since the catalyst system itself undergoes a wide variety of intermediate states during the reaction, the analysis of each intermediate species of catalyst material is the first step in understanding the reaction mechanism. To understand the reaction mechanism of efficient catalyst systems for water splitting reaction, characterization of both the initial and intermediate states of the catalyst system is performed by various in situ/ex situ spectroscopy analysis. Chapter 2 investigates sub-10 nm sized Mn3O4 nanoparticle (NPs) for electrocatalytic water oxidation reaction under the neutral pH condition. Through the in situ Raman spectroscopy analysis, we found out that the initial Mn3O4 NPs undergoes totally different reaction mechanism depending on the type of anion in the electrolyte. Further ex situ electron paramagnetic resonance (EPR), in situ X-ray absorption near edge structure (XANES), in situ UV-Vis spectroscopy analysis reveal that the anion with proton accepting ability is essential for efficient water oxidation reaction with Mn3O4 NPs catalyst by generating high-valent Mn-oxo species through the proton-coupled electron transfer manner. Based on the above-mentioned mechanism, we have shown that the high-valent Mn-oxo species is a key intermediate species that determines the overall reaction rate, and in Chapter 3, we conduct studies to control this reaction intermediate species. By substitute Ni atoms to Mn3O4 NPs lattice, new intermediate signal is detected by ex situ EPR measurement. EPR simulation and DFT calculation show that substituted Ni can induce the compressed distortion in the active Mn site rather than directly participate in the reaction, forming new intermediate species with low spin electronic configuration (Mn(IV)=O, S=1/2). Chapter 4 investigates single atom Cu/TiO2 for photocatalytic hydrogen generation reaction. Single Cu atoms are successfully substituted to the Ti sites in anatase crystal structure of TiO2 material by modified wrap-bake-peel process. Synthesized Cu/TiO2 system undergoes unique reversible and cooperative photoactivation process. From ex situ UV-Vis, photoluminescence, XANES, and EPR spectroscopic analysis and DFT calculation, we found out that the redox state of single Cu atom is reversible changed, which modulate the optoelectronic properties and photocatalytic activity of the overall Cu/TiO2 system. In conclusion, we try to characterize and control the intermediate species of the catalyst systems for water splitting reaction. Our study provides a significant mechanistic insight for water splitting reaction and suggest the direction of the catalyst system design that could extend the boundaries of conventional heterogenous catalyst system. 원하는 반응에 적합한 촉매 시스템을 개발하는 것은 산업적으로, 과학적으로 중요한 의미를 갖는 중요한 목표이다. 특히 태양 에너지를 수소 에너지원으로 바꿀 수 있는 광-/전기-화학 물분해 촉매 시스템은, 인류가 당면한 환경 및 에너지 문제를 해결하고 지속가능한 미래 에너지 시스템을 달성하기 위한 이상적인 기술로 매우 각광받고 있다. 많은 계산결과와 실험 결과들로 뒷받침된 descriptor 기반의 volcano 촉매 시스템 디자인 접근을 통해 촉매 시스템의 효율은 점진적으로 개선되어 왔다. Descriptor 기반의 volcano 디자인은 촉매 시스템 전반에 대한 이해도를 높이고 시스템 효율 증가에 기여해 왔지만, volcano limitation 을 넘어 가격 경쟁력을 갖춘 촉매 시스템 효율 달성을 위해서는 새로운 촉매 시스템 디자인 접근법이 필요한 상황이다. 이를 위해서는 촉매 시스템의 반응 메커니즘에 대한 구체적인 이해가 필수적이다. 보통 촉매 반응 사이클은 단순한 한 단계의 스텝이 아니라, 활성화 과정, 반응물 흡착 과정, 생성물 탈착 과정, 재생 과정 등의 여러가지 복잡한 스텝으로 이루어져 있다. 그리고 이 다양한 과정에서 촉매 물질 자체가 다양한 형태의 중간 상태를 거치게 되고, 이 각각의 중간 상태를 분석하는 것은 반응 메커니즘 이해의 첫 걸음이 될 것이다. 본 연구에서는 특히 효율 높은 물분해 반응 촉매 시스템에 다양한 실시간 분광학 분석법을 적용해 촉매 물질의 초기 상태와 다양한 중간 상태를 분석하여 반응 메커니즘을 이해하고자 하였다. Chapter 2 에서는, 중성 pH 조건의 전기화학 물산화 반응용 10 nm 이하의 크기의 Mn3O4 나노입자 시스템에 대한 연구를 진행하였다. 실시간 Raman 분광학 분석을 통해, 전해질의 음이온 종류에 따라서 같은 Mn3O4 나노입자도 완전히 다른 반응 메커니즘을 갖는 것을 발견했다. 추가적으로, 실시간 EPR, XANES, UV-Vis 분광학 분석을 통해 Mn3O4 나노입자는 proton accepting 능력을 가진 음이온이 존재하는 경우 proton-coupled electron transfer 를 통해 high-valent Mn-oxo 종을 형성하며 물산화 반응을 진행하는 것을 밝힐 수 있었다. 위에서 밝힌 반응 메커니즘을 기반으로 Chapter 3 에서는, 전체 촉매 반응 속도를 더욱 향상시키기 위해 중요 중간체인 high-valnet Mn-oxo 종을 제어하는 연구를 진행하였다. Mn3O4 나노입자 격자구조에, Ni 원자를 치환시켜주는 경우, 물산화 반응 조건 하에서 새로운 형태의 EPR 신호를 관찰 할 수 있었다. SQUID 분석, EPR 시뮬레이션, DFT 계산을 통해 치환된 Ni 원자라 주변 Mn 활성점의 구조를 압축시켜 low spin electronic configuration 을 갖는 Mn(IV)=O (S=1/2) 중간체를 형성할 수 있다는 것을 확인하였다. Chapter 4 에서는 광촉매 수소생산용 Cu/TiO2 촉매 시스템에 대한 연구를 진행하였다. Modified wrap-bake-peel 공정을 통해 성공적으로 Cu 단원자를 anatase TiO2 나노입자 격자내의 Ti site 에 치환시킬 수 있었다. 이렇게 합성된 Cu/TiO2 광촉매 시스템은 독특한 reversible and cooperative 광활성 과정을 거치며 매우 높은 광촉매 수소생산 활성을 보였다. UV-Vis, photoluminescence, XANES, EPR 분석을 통해, 단원자 Cu 의 산화가가 가역적으로 2+, 1+ 사이를 오가며 주변 TiO2 격자에 distortion을 유도하고 물질의 optoelectronic 성질 및 광촉매 활성을 제어한다는 것을 확인하였다. 종합적으로 본 연구에서는 물분해 반응용 촉매 시스템의 다양한 중간 상태를 분석하고 제어하고자 하였다. 이러한 연구 결과들은 물분해 반응 메커니즘 이해에 매우 중요한 기본 바탕이 되며 기존의 비균질 촉매 시스템의 한계를 뛰어 넘는 촉매 시스템 디자인을 위한 방향성을 제시할 수 있을 것으로 기대한다.

Efficient Synthesis of Benzoylacetonitrile in a Continuous Flow Reaction System

Joon Young Kim 고려대학교 대학원 2022 국내석사

Benzoylacetonitrile is a highly reactive material that can be converted into various heterocyclic compounds and is used as a building block in many organic chemical reactions. Many methods have been reported for the synthesis of benzoylacetonitrile. In this study, using C-N bond activation of N, N-dimethylbenzamide in the presence of LiHMDS for the synthesis of benzoylacetonitrile. The disadvantage of this reaction is that it takes long time to obtain a high yield of product. To solve this problem, a continuous flow reaction system was used. A continuous flow reaction system has advantages in heat and material transfer as compared to a batch reactor, and has advantages in that temperature and pressure conditions that are difficult to apply to a general batch reactor can be applied. Also, by applying the reaction to a continuous flow reaction system, the actual process suitability of the reaction can be predicted. As a result, by converting the benzoylacetonitrile synthesis reaction from a batch reactor to a continuous reaction system, the reaction time was reduced and a higher product yield was obtained. In addition, the suitability of the system was confirmed through synthesis using other amides. Benzoylacetonitrile은 반응성이 높은 물질로, 다양한 heterocyclic compounds 로 전환될 수 있어, 많은 유기 화학 반응에서 building block으로 이용된다. Benzoylacetonitrile의 합성에는 많은 방법들이 보고되어왔다. 본 연구에서는 새로운 방법인 LiHMDS 존재하의 N,N-dimethylbenzamide의 C-N 결합 활성화를 이용하여, N,N-dimethylbenzamide와 Acetonitrile로 Benzoylacetonitrile 합성을 진행하였다. 이 반응은 높은 수율을 얻기까지 시간이 많이 필요하다는 단점이 있다. 이러한 문제를 해결하기 위해 연속 흐름 반응 시스템을 이용하였다. 연속 흐름 반응 시스템은 회분식 반응기와 비교하여, 열 및 물질 전달에 이점이 있고, 일반적인 회분식 반응기에는 적용하기 힘든 온도와 압력 조건을 적용할 수 있다는 장점이 있다. 또한, 연속 흐름 반응 시스템으로의 적용을 통해, 반응의 실제 공정 적합성을 미리 예상해볼 수 있다. 결과적으로, Benzoylacetonitrile 합성반응을 회분식 반응기에서 연속반응 시스템으로 전환하여, 반응 시간을 줄였고, 생성물의 더 높은 수율을 얻어냈다. 또, 다른 아마이드를 이용한 합성을 통해 시스템의 적합성을 확인하였다.

Reaction mechanism of the oxidant step in atomic layer deposition based on quantum chemical calculation

서승기 Graduate School, Yonsei University 2021 국내박사

The semiconductor device scaling down occurred with to Moore's Law. As the size of semiconductor devices is reduced to sub-10 nm scale, it is essential to deposit a dielectric layer and a metal thin film in a complex structure for fabrication of semiconductor device. Atomic layer depsotion (ALD) is vapor phase deposition technique based on two kinds of half-reaction; i) self-limited surface adsorption of precursor on substrates, ii) self-limited chemical reaction between reactant and surface adsorbed precursor. The film is depostied through sequential exposure of precursor and reactant. ALD is in the spotlight as it is considered a suitable deposition method for semiconductor device fabrication owing to its thickness controllability with sub-nm scale and excellent conformality in a 3D structure. Since ALD is based on surface chemical reaction, surface characteristics of the substrate and the types of precursor or reactant could affect material properties of ALD deposited films and the reaction mechanism of ALD processes. Therefore, it is important to select suitable precursors and reactants. In previous studies for ALD process development, the researchers investigated the effect of various precursors and reactants on the ALD process by the way of trial and error. However, this method has a limitation in that it requires a lot of manpower and time. In the 2010s, the development of materials and processes through computer simulation using computer simulations has attracted attention in the materials industry. Among various computational simulation methods, Density Functional Theory (DFT) is a quantum chemical simulation method that could predict the chemical reaction. Since the thermal stability of the precursor, the precursor adsorption energy, and the reaction energy between the reactant and surface adsorbed precursor could be calculated by using DFT, the DFT calculation is a very promising method for investigating the ALD reaction mechanism. In this dissertation, we investigated the method of developing the ALD process through understanding the reaction mechanism with the various reactants through the DFT calculation. We investigated reaction mechanism between various reactants and surface adsorbed TMA precursor for selection of suitable reactant according to various application fields of Al2O3. For development of low temperature process, we proposed detailed atomistic mechanisms for oxidation reactions during ALD of Al2O3 using various oxidants: H2O, H2O2, and O3. All the oxidants have shown feasibly to oxidize the surface CH3 group which is the major surface species after adsorption of TMA, into surface OH. Comparison of the reaction pathways indicate that while the activation energy of the oxidation reactions decreases in the order of H2O > H2O2 > O3, the exothermicity of the reactions show the opposite trend: H2O < H2O2 < O3. In addition, ALD process with H2O2 reactant could generate H2O by-product, which could condense at low temperature condition. Then, we concluded O3 is the most suitable reactant for low temperature ALD Al2O3 process. And we also investigated reaction mechanism of ALD Al2O3 with alcohol reactants and developed non-hydrolytic ALD Al2O3 process. We suggested various reaction mechanism and compared reaction pathways of the reactions. Based on the calculation results, we discovered that the β-hydrogen (β-H) of EtOH and n-PrOH could easily oxidize surface methyl groups (Al–CH3) into surface hydroxyl groups (Al–OH). Based on the density functional theory (DFT)-calculated chemical mechanisms, we suggest that EtOH is a good candidate for ALD of Al2O3 with TMA. To validate our proposed reaction mechanism, we developed ALD Al2O3 processes using alcohol oxidants. Since the ALD process with EtOH oxidant showed a 0.96 Å/cycle growth rate and a low level of carbon impurities, and superior electrical properties EtOH is the most suitable alcohol oxidant for ALD of Al2O3. In this research, we investigated the effect of the surface characteristics and the types of precursors or reactants on reaction mechanism during ALD process by using quantum chemical simulation. Based on the theoretical studies, we developed and optimized ALD process for various ALD applications. Therefore, this study is an important study to reduce the manpower and time consumed in previous ALD studies which investigated by using the trial & error method. 반도체 소자의 구조는 Moore 법칙에 따라 지속적으로 미세화 되고 있다. 반도체 소자의 미세화가 10 nm 수준 이하로 진행됨에 따라 반도체 소자 제작을 위해 미세화된 구조에서의 절연층 및 금속 박막 증착 기술이 필수적인 상황이다. 원자층 증착법은 전구체와 기판 사이의 표면 흡착 반응, 흡착된 전구체와 반응물 사이의 표면 화학 반응 두 가지 자기제한적 표면 화학 반응 기반의 증착 방법으로, 전구체(precursor)와 반응물(reactant)를 분리하여 순차적으로 기판 표면에 노출시켜 박막이 형성된다. 원자층 증착법은 원자 단위에서 박막의 두께 조절이 가능하고 3 차원 구조에서의 우수한 계단 도포성을 보이기 때문에 반도체 소자 제작용 공정에 적합한 증착 방법으로 여겨져 매우 각광받고 있는 기술이다. 원자층 증착법을 이용하여 증착된 박막의 물성은 전구체 및 반응물 종류에 따라 달라질 수 있고, 물질 종류 및 표면 상태에 따라 표면 화학 반응 메커니즘도 상이하기 때문에, 적합한 전구체, 반응물의 종류를 선별하는 것이 중요하다. 이를 위해서는 물질의 종류 및 이에 따른 원자층 증착 공정의 반응 메커니즘의 이해가 필수적이다. 기존에 진행된 원자층 증착법 공정 개발 연구에서는 전구체 및 반응물의 종류에 따라 직접 실험을 진행해보고 결과를 확인하는 방식으로 연구가 진행되어 왔다. 그러나 이러한 방식은 많은 인력과 시간이 필요하다는 한계가 있다. 2010 년대에 들어 소재산업에서 컴퓨터 시뮬레이션을 이용한 전산 모사를 통한 소재 및 공정의 개발이 관심을 받고 있다. 다양한 전산 모사 방법 중 밀도범함수 이론(Density Functional Theory, DFT)은 양자역학 적으로 원자 단위에서의 반응을 계산하는 방식으로, 이를 이용할 경우 전구체의 열적 안정성, 표면 흡착 에너지, 반응물과의 반응 에너지 등의 계산이 가능하기 때문에 원자층 증착법의 반응 메커니즘을 연구하는 데에 다양하게 적용되고 있다. 본 논문에서는 원자층 증착법 공정 개발을 위해 밀도범 함수 이론 계산을 통해 공정의 목적에 맞는 반응물을 선정하기 위해 다양한 반응물에 따른 반응 메커니즘을 이해하고 이를 통해 실제 공정의 개발을 진행하는 방법에 대하여 연구하였다. 이를 위해 본 연구진은 다양한 Al2O3 적용 분야에 따른 반응물의 선별 및 개발을 위해 흡착한 TMA 전구체와 다양한 반응물 종류에 따른 반응 메커니즘에 대하여 연구하였다. 저온 공정을 위해서, H2O, H2O2 및 O3 반응물에 따른 반응 메커니즘에 대한 연구를 진행하였고, 이를 통해 O3 반응물이 가장 낮은 activation barrier 을 갖고 있으며, 반응 중간생성물로 H2O 를 생성하지 않기 때문에 저온 공정에 가장 적합한 반응물임을 밝혔다. 이외에도 H2O 반응물의 높은 반응성으로 사용이 어려운 분야로의 적용을 위한 무수화 공정의 개발을 위해 알코올 기반의 반응물을 이용한 원자층 증착 공정의 다양한 반응 경로를 고려하여 반응 메커니즘을 규명하였다. 특히, 알코올 분자 내에 존재하는 beta-Carbon 이 원자층 증착 공정에 중요한 역할을 한다는 것을 밝혔으며, 이를 통해 다양한 알코올을 이용하여 원자층 증착 공정을 개발하고, 박막 물성에 대해 연구하였다. 본 연구는 원자층 증착 공정 중, 반응물 종류에 따른 표면 화학 반응을 이해하고 이를 통해 적합한 물질의 선별 및 최적화된 공정의 개발을 진행하였다. 따라서, 본 연구는 기존에 진행되던 trial & error 방식의 연구에서 소모되는 인력 및 시간을 단축하기 위한 중요한 연구이다.

Automated Exploration of Uncertain Deep Chemical Reaction Networks

Woulfe, Michael Purdue University ProQuest Dissertations & Theses 2024 해외박사(DDOD)

Algorithmic reaction explorations based on transition state searches can now routinely predict relatively short reaction sequences involving small molecules across a variety of chemical domains, including materials degradation, combustion chemistry, battery performance, and biomass conversion. Mature quantum chemistry tools can comprehensively characterize the reactivity of species with efficiency and broad coverage, but consecutive characterizations quickly encounter prohibitive costs of reactant proliferation, spurious characterization of irrelevant intermediates, and compounding uncertainties of quantum chemical calculations deep in a network. Application of these algorithms to deeper chemical reaction network (CRN) exploration still requires the development of more effective, comprehensive, and automated exploration policies.This dissertation addresses the challenge of exploring deep chemical reaction networks (CRNs) in complex and chemically diverse systems by introducing Yet Another Kinetic Strategy (YAKS), an automated algorithm designed to minimize the computational costs of deep exploration and maximize coverage of important reaction channels. YAKS demonstrates that microkinetic simulations of the nascent network are cost-effective and able to iteratively build deep networks. Key features of the algorithm are the automatic incorporation of expanded elementary reaction steps, compatibility with short-lived but kinetically important species, and the incorporation of rate uncertainty into the exploration policy. The automatically induced expansion of reaction mechanisms gives YAKS access to important chemistries that other algorithms ignore, while also maintaining the ability to limit expensive forays into kinetically irrelevant regions of the CRN that would stymie previous methods. Instead of conducting a greedy exploration, YAKS biases network topography to probe beyond short-lived but kinetically important species, which enables YAKS to explore important endergonic reactions deep into the CRN. YAKS further induces rate uncertainty into an ensemble of microkinetic simulations, which positively influences intermediate prioritization deep in a network.Algorithm effectiveness was validated in a case study of glucose pyrolysis, where the algorithm rediscovers reaction pathways previously discovered by heuristic exploration policies and also elucidates new reaction pathways to experimentally obtained products. The resulting CRN is the first to connect all major experimental pyrolysis products to glucose. Additional case studies are presented that investigate the role of reaction rules, rate uncertainty, and bimolecular reactions. These case studies show that na\\"ive exponential growth estimates can vastly overestimate the actual number of kinetically relevant pathways in physical reaction networks. The excellent performance of YAKS demonstrates the ability of automated algorithmic methods to address the gaps outlined above.The power of YAKS was then demonstrated on radically distinct chemistry from the validation study, chemical warfare agents (CWAs). Despite the almost uniform ban on the use of chemical agents and the widespread neutralization of stockpiles due to treaties, CWAs continue to pose a grave threat around the world. Rogue states, terrorist organizations, and lone wolf terrorists have all conducted CWA attacks within the past few decades. These circumstances make it necessary to prepare against and forensically evaluate the use of CWAs without direct experimentation. YAKS was applied to elucidate degradation reaction networks of three prominent CWAs, mustard gas (SM, HD), sarin (GB), and VX, and identified a range of possible degradant products of real world use cases. This dissertation also computationally interpreted the most common mechanism of action (MoA) associated with each CWA and examined their hydrolysis networks as a method to neutralize these agents. Additionally, agent stability was evaluated during extended microkinetic modeling in arid and humid scenarios, highlighting the potential for computational simulation approaches to fill a capability gap in the broader field of chemical defense.This dissertation advanced automated CRN exploration, but considerable gaps remain. Future research directions include the accuracy gaps of both density functional theory and conformational sampling on energy calculations. Incorporation of machine learning (ML) methods can accelerate the costly reactivity characterization process, but ML models still require vast amounts of data. A recently released dataset comprehensively explored over 175,000 graphically defined reactions of moderately-sized C, H, O, and N containing molecules. While models trained on such data could readily be applied to glucose pyrolysis systems, chemical agents involve a much wider array of chemistry including Cl, S, P, and considerable quantities of radical and charged species. More comprehensive datasets are required to train a general ML model capable of accelerating geometry or energy calculations. Additionally, microkinetic modeling is hindered by software implementations that are unable to explore diverse chemistry such as multiphase reactions. In light of this, further improvements in exploration policies, reaction prediction algorithms, and simulation software make it feasible that CRNs might soon be routinely predictable in many additional contexts.

Characterization of Melanoidins based on Amadori and Heyns Rearrangement Products by Racemization in Maillard Reaction Scheme

김지상 경희대학교 2008 국내박사

본 연구에서는 환원당인 포도당, 과당과 L형, D형 아미노산에 의해 형성되는 아마도리 화합물과 헤인스화합물의 비효소적 갈변 과정을 통해 형성되는 멜라노이딘의 특성을 규명하였다. 따라서 본 연구는 (1) 모델 마일라드 시스템을 통한 당의 엔올화와 아미노산의 라세미화에서의 pH의 효과, (2) 투석 과정을 통해 형성된 멜라노이딘의 항산화 효과에서의 pH의 효과, (3) 모델 시스템을 통해 형성된 멜라노이딘의 색 형성에서의 pH의 효과, (4) FT-IR과 XRD를 통한 멜라노이딘의 구조적 특성 평가, (5) 모델 마일라드 시스템에서의 furfural compounds의 형성 평가를 연구하였으며 그 결과는 다음과 같다. 1. pH 증가에 따라 당의 엔올화 반응은 포도당 시스템에서 더 쉽게 나타났으며 아미노산의 라세미화는 L형의 아미노산이 D형으로 전환되는 비율이 큰 것으로 나타났다. 또한 pH 증가에 따라 멜라노이딘의 형성은 증가하였으며 이성질체에 따른 멜라노이딘 형성의 차이는 없었다. 2. 멜라노이딘의 항산화 효과는 chelating activities를 제외하고 투석 후 급격히 증가하였으며 Glc(Fru)/Gly system으로부터 형성된멜라노이딘은 pH 7.0에서 효과가 가장 크게 나타난 반면 Glc(Fru)/L(D)-lysine 으로부터 형성된 멜라노이딘은 pH 증가에 따라 항산화 효과가 감소하는 것으로 나타났다. 또한, 이성질체에 따른 멜라노이딘의 항산화 효과의 차이는 없었다. 3. 멜라노이딘의 extinction coefficients는 pH 7.0에서 이성질체 간의 차이가 적은 것으로 나타났으며 색 형성 평가 결과 멜라노이딘의 주된 색소는 파랑색으로 나타났고 pH 증가에 따라 노란색이 증가하는 것으로 나타났다. 또한, 이성질체에 따른 멜라노이딘의 색 형성의 차이는 없었다. 4. FT-IR 결과, 멜라노이딘의 화학구조는 상당량의 OH, NH, CH2, CH3, amide I, amide II 그리고 amide III groups이 존재하며 aromatic furanic compound의 결합도 존재하는 것으로 나타났다. 또한 XRD 결과, 멜라노이딘의 주된 결정상은 10 ~ 21°(2θ) 범위에서 존재하며 pH 증가에 따라 멜라노이딘의 결정상의 강도는 증가하였으며 이성질체의 차이는 없었다. 5. 모델 마일라드 시스템을 통해 형성된 furfural compounds의 평가 결과, 산성조건에서는 hydroymethylfurfura1 (HMF)의 형성이 증가하였으며 염기성조건에서는 furfuryl alcohol (FFA)와 2-furaldehyde (F)가 형성되는 것으로 나타났다. 이상의 결과, 아마도리 화합물과 헤인스 화합물의 비효소적 갈변 과정을 통해 형성되는 멜라노이딘은 pH 변화에 따라 그 특성이 다르게 나타나며 특히 저분자량의 멜라노이딘의 경우 chelating activity가 더 우수하였다. 또한 마일라드 반응의 연구에 있어서 당의 엔올화와 아미노산의 라세미화 반응은 또 하나의 중요한 영향 요인으로 여겨지며 멜라노이딘의 기능적 측면에서 제과제빵과 장류산업에 적용이 가능할 것으로 사려된다. The objective of this study was to investigate the characterization of melanoidins due to the Maillard reactions, which based on enolization and racemization of glucose (or fructose) with D (or L) forms of amino acid while heating as a function of pH. In the present study, remarkable enolization of sugars was observed in the course of the Maillard reaction. The degree of sugar enolization was increased as the pH increased, which was especially higher in the fructose system than in the glucose system. On the other hand, enolization of sugars with amino acid during heating was higher in the glucose system than in the fructose system. In addition, the racemization of amino acid was higher in glucose-based system. The formation of isomer was easier with the L-amino acid than the D-amino acid. The relative amounts of isomers in fructose with lysine were increased with the increase of pH, regardless of enantiomer form. While glucose with D or L lysine systems were not affected by the pH. Development of browning during heating was more significant (p<0.05) in the sugar-amino acid model system especially with fructose compared to glucose solution alone, which was affected by the pH. The L- and D- isomers showed different absorption with similar shape in the UV-visible spectra. Every peak has a stable absorbance in the range of 260 to 320 nm, which is the characteristic of melanoidins. In addition, antioxidative activities of melanoidins were different before and after dialysis. Antioxidative activities of melanoidins after dialysis were significantly (p<0.05) higher than those before dialysis, except for ferrous ion chelating activities. At pH 7, antioxidative activities of melanoidins from glucose with the glysine system were greater compared to those at pH 4 and pH 10. Moreover, the difference in the extinction coefficients of melanoidins with amino acids enantiomers became less significant at pH 7. On the other hand, antioxidative activities of melanoidins with lysine were decreased as the pH increased, regardless of the type of sugar. In addition, melanoidins that formed with D-isomers had similar antioxidative activities to those of L-isomers. Most of the melanoidins were shown as blue-green locus at the wavelength of 475 nm. The color of melanoidins was grouped within a narrow band from the blue-green spectrum to the direction of yellow-red locus as the pH increased. Especially, the yellowness increased in the glucose-based system with the increase in pH. Furthermore, the difference became less significant with amino acids enantiomer. The structure of melanoidins was composed of OH, NH, CH2, CH3, amide I, amide II and amide III groups. Particularly, the structure of melanoidins formed from the glucose-based system had a stronger union than that of the fructose-based system. The chemical composition of melanoidins was also observed in the band of aromatic furanic or conjugated compounds. The crystallinity of melanoidins products was formed in the 10-21° (2θ) range. As the pH increased, the intensity of the crystallinity of melanoidins increased as well. Similar crystallinity of melanoidins was formed from D or L -isomer with a different intensity. In order to quantify the furfural compounds as the indicator of the advanced Maillard reaction, hydroymethylfurfura1 (HMF) was formed in the acidic condition, while furfuryl alcohol (FFA) and 2-furaldehyde (F) were formed in the basic condition. The results of the present study indicate that the pH affected the enolization and racemization during the Maillard reaction, which caused the different characteristic of melanoidin. In addition, the results of this study can apply this functional aspect of melanoidin, particularly in the industries of bakery and fermented soy sauce. In the future, enolization and racemization must be considered in the kinetic study of Maillard reactions.

플루오르화 가소제와의 아자이드-알카인 클릭반응을 적용한 폴리우레탄 결합제의 합성 및 물성 : Synthesis of Polyurethane Binders Utilizing Azide-Alkyne Click Modification with Fluorinated Plasticizers and Their Properties

장선옥 대구대학교 2015 국내석사

In development of energetic materials, energetic plasticizer as an additive is facing lots of challenges such as high and secure energy output, efficient plasticizing ability and long sustained service life. The way to meet the requirements about providing high energy is to modify plasticizer by using energetic functional groups. But the energetic functional groups, such as nitrate, nitro, nitrite and azido groups, show high impact sensitivity, instability at high temperature or easy oxidation under air atmosphere, and these properties cause the safety problem during the process of manufacture, transportation, usage and storage. So plasticizers with new concept was studied in this research. The energy output was by the reaction between the new concept of plasticizer and other material, such as thermite reaction. Thermite reaction is used to describe exothermic reactions involving reduction of oxides with aluminum (Al) to form aluminum oxide and reduction of element. The use of fluorine or its derivatives as oxidizers in various propellants and explosives has been recognized for many years. The reaction of fluorine and its derivatives with metals and metal hydrides is of interest in various pyrotechnics. Al reacts with decomposition products of fluorine containing polymers to produce metal fluorides, generally in the gaseous state yielding comparatively high flame temperature and enthalpy release. Therefore the fluorine-containing group was proposed to use as new concept of energetic functional group. The problem of leaching, migrating and evaporating could be solved by strengthening the force between plasticizer and polymer. By referencing the idea of reactive plasticizer, a new form of reactive plasticizer with suitable molecular weight (MW) was designed to resist leaching, migrating and evaporating while had excellent plasticization. Efficient and effective “click” reaction was used to form a chemical bond between plasticizer and polymer. Hence three types of six different reactive plasticizers (RPs), long fluorinated ester linkage RPs, short fluorinated ester linkage RPs and short fluorinated formal linkage RPs, have been synthesized by combining fluorine-containing groups and clickable alkyne groups. As well as, the ability of RPs on improving processability of prepolymer and the effect on thermal and mechanical property after being incorporated with polyurethane (PU) binders were investigated. RPs present low viscosity (20 cP to 30 cP at 30 °C and 6 cP to 10 cP at 60 °C), low glass transition temperature (below -100 °C) and acceptable thermal stability, as well as high reactivity with azide groups of poly(glycidyl azide-co-tetramethylene glycol) (PGT) polymers. The four short fluorinated ester and formal linkage RPs showed good miscibility with PGT polyols and decreased the viscosity of PGT polyols. The viscosity of PGT polyol dramatically decreased after mixing 50 wt% of RPs. The extent of azide-alkyne click reaction between RP and PGT prepolymer could reach 100%. The reactivity of RP was proportional to electrophilic ability of alkynyl group. The ester linkage RPs and shorter intramolecular distance between EWG and alkynyl (d=1) RPs showed higher reactivity. The thermite reaction between PGT-RP and n-Al was assessed by DSC (Al crucible) and DSC (high pressure crucible). 20 wt% n-Al mass loading was selected to apply into PU binders. The investigation of energetic performance about long fluorinated ester linkage RP, E-15F-2, proved the high content of fluorine made a contribution to higher energetic performance. RP was incorporated in PGT-based PU binder with aluminum nanopowder (n-Al) by in-situ "click" reaction during PU reaction. After getting PU binder, mechanical properties of RP-incorporated PGT-based PU binders with n-Al were investigated by means of measuring the tensile strength and strain. The mechanical properties were changed after incorporating with RPs. The glass transition temperature (Tg) of RP-incorporated PGT-based PU binders with n-Al was measured by differential scanning calorimetry (DSC). The triazole groups which were formed by “click” reaction appeared to affect on the thermal property, presenting higher Tg than PGT base PU binder. As well as, the thermal stability was analysed by thermogravimetric analysis (TGA) with temperature from 50 °C to 900 °C. Compared to thermal maximum decomposition temperature (Td,max) of PGT-based PU binder with n-Al aroud 240.0 °C, the Td,maxs of RP-incorporated PGT-based PU binders with n-Al were around 380 °C, implying that the incorporating of RPs could enhance the thermal stability of PU binders. The energetic performance of RP-incorporated PGT-based PU binder and n-Al was assessed by DSC (Al crucible) and DSC (high pressure crucible). The PGT(5/5) PU binder system exhibited more excellent energrtic performance than PGT(3/7) PU binder system because the larger fluorine content. 가소제는 낮은 유리전이온도, 낮은 점도, 낮은 누출특성 및 높은 열 안정성을 가져서 고분자의 유연성 및 가공성 향상에 기여한다. 이러한 요구 특성들은 일반적으로 많은 경우에 상충되므로, 최적의 가소제를 적용하는데 어려움을 가진다. 최근 고에너지 물질 분야에서 에너지화 가소제에 대한 연구가 많이 진행되고 있으며, 다양한 구조의 에너지화 가소제가 현재 합성 및 적용되고 있다. 현재까지 합성된 에너지화 가소제들은 가소제로서의 특성을 충족시켜주고 있을 뿐 만 아니라, 높은 에너지 공급에 기여하고 있다. 그러나, 에너지화 가소제는 물리적으로 고에너지 물질에 분산되어 있으므로, 시간이 지남에 따라 에너지화 가소제의 누출이 발생함으로써 장기적인 저장 및 안정성에 큰 문제점을 지니고 있는 단점이 있다. 또한 에너지화 가소제에서 에너지 증대에 기여하는 에너지 그룹은 열 안정성의 감소, 충격감도의 증가 등 고에너지 물질의 민감도를 증가시키는 단점도 지니고 있다. 본 연구에서는 이러한 단점들을 보완하기 위한 새로운 반응형 가소제를 디자인하고 합성하고자 하였다. 신규 반응형 가소제의 구조적 특징으로는, 첫째 뛰어난 가소화 효과를 부여하기 위해서는 고분자 결합제와의 혼화성이 중요하므로 에스터 또는 에테르 화학구조를 도입하였다. 둘째 반응형 관능기인 알카인 구조를 가소제에 도입하여 고분자 결합제의 곁가지에 클릭반응을 통하여 도입됨으로서 시간에 따른 가소제의 누출 문제를 해결하고자 하였다. 셋째 기존 에너지화 가소제에 도입되는 에너지화 그룹을 대체하여 일상적인 조건에서는 inert한 물질로 존재하지만 고에너지 물질이 작동하는 조건에서 추가적인 에너지를 공급할 수 있는 관능기를 도입하였다. 이러한 잠재적 에너지화 반응으로 thermite 반응을 이용하고자 하였으며 이를 위하여 반응형 가소제에 플루오르기를 도입하였다. 기본적으로 3가지 형태로 분류될 수 있는 6종류의 반응형 가소제를 합성하였다. Long fluorinated ester linkage 반응형 가소제, short fluorinated ester linkage 반응형 가소제와 short fluorinated formal linkage 반응형 가소제를 합성하였다. 이들 반응형 가소제들은 낮은 점도 (20~30 cP at 30 oC,6~10 cP at 60 oC),낮은 유리전이온도 (-100 oC이하), 적합한 열 안정성 및 poly(glycidyl azide-co-tetramethylene glycol) (PGT)의 아자이드 그룹과의 매우 높은 클릭반응성을 가지고 있음이 확인되었다. Short fluorinated ester linkage 반응형 가소제와 short fluorinated formal linkage 반응형 가소제는 PGT prepolymer와 뛰어난 상용성을 나타내었으며, 50 중량 퍼센트의 이들 반응형 가소제를 혼합했을 때 PGT prepolymer의 점도가 급격히 하락됨을 확인하였다. 반응형 가소제와 PGT prepolymer의 아자이드-알카인 클릭반응도는 100%에 도달하였다. 이때 반응형 가소제의 반응성은 alkynyl group의 친전자성에 비례하였다. 반응형 가소제 구조내에 있는 EWG와 alkynyl group 사이에 1개의 methylene spacer가 있는 반응형 가소제가 높은 반응성을 나타내었다. 반응형 가소제와 반응한 PGT와 나노 알루미늄과의 thermite 반응은 일반 Al crucible을 사용한 DSC와 고압 crucible을 사용한 DSC를 사용하여 각각 평가하였다. 이 평가에서 20 중량 퍼센트의 나노 알루미늄 함량을 폴리우레탄 바인더에 적용하기로 결정하였다. PGT-based 폴리우레탄 결합제 합성하는 폴리우레탄 반응에 반응형 가소제와 나노 알루미늄을 혼합하여 in-situ 클릭반응을 수행하였다. 합성된 폴리우레탄 결합제의 기계적 물성은 반응형 가소제의 첨가에 의해 변화하였으며, 유리전이온도도 합성된 폴리우레탄 결합제내에 생성된 triazole group에 의해 증가함이 관찰되었다. 열 안정성은 TGA를 이용하여 평가하였으며, 합성된 폴리우레탄 결합제의 열 분해온도는 반응 전의 PGT prepolymer의 240 oC에서 380 oC로서 증가하였으며 이는 반응형 가소제의 도입에 의해 생성된 triazole 관능기에 의한 증가효과로 판단되었다. 나노 알루미늄과 혼합된 RP-incorporated PGT-based 폴리우레탄 결합제의 에너지 성능을 평가한 결과에 의하면, fluorine 함량과 보다 많은 반응을 할 수 있는 PGT(5/5) prepolymer를 사용하여 합성한 폴리우레탄 결합제가 PGT(3/7)을 적용한 시스템보다 높은 에너지 성능을 나타냄을 확인하였다.