scholarly journals Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 537 ◽  
Author(s):  
Ahmed Issa ◽  
Adriaan Luyt
Keyword(s):  
Density Functional ◽  
Early Stage ◽  
Reaction Medium ◽  
Reaction Rates ◽  
Dft Methods ◽  
Functional Theory ◽  
Kinetics Of Polymerization ◽  
Leaving Group ◽  
Technical Article ◽  
Kinetics Of

Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which the kinetics of alkoxysilanes polymerization are discussed. The kinetics of polymerization are controlled by primary factors, such as catalysts, water/silane ratio, pH, and organo-functional groups, while secondary factors, such as temperature, solvent, ionic strength, leaving group, and silane concentration, also have an influence on the reaction rates. Experiments to find correlations between these factors and reaction rates are restricted to certain conditions and most of them disregard the properties of the solvent. In this review, polymerization kinetics are discussed in the first two sections, with the first section covering early stage reactions when the reaction medium is homogenous, and the second section covering when phase separation occurs and the reaction medium becomes heterogeneous. Nuclear magnetic resonance (NMR) spectroscopy and other techniques are discussed in the third section. The last section summarizes the study of reaction mechanisms by using ab initio and Density Functional Theory (DFT) methods alone, and in combination with molecular dynamics (MD) or Monte Carlo (MC) methods.

scholarly journals Platinum catalyzed hydrodeoxygenation of guaiacol in illumination of cresol production: a density functional theory study

2017 ◽  
Vol 4 (11) ◽  
pp. 170650 ◽  
Author(s):  
Anand Mohan Verma ◽  
Nanda Kishore
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Reaction Rates ◽  
Transportation Fuel ◽  
Phenolic Fraction ◽  
Functional Theory ◽  
Heating Value ◽  
Wide Range ◽  
Bio Oil ◽  
Kinetics Of

The unprocessed bio-oil obtained by the pyrolysis of lignocellulosic biomass comprises hundreds of oxy-components which vitiate its quality in terms of low heating value, low stability, low pH, etc. Therefore, it has to be upgraded prior to its use as transportation fuel. In this work, guaiacol, a promising compound of the phenolic fraction of unprocessed bio-oil, is considered as a model component for studying its hydrodeoxygenation over a Pt 3 catalyst cluster. The production of catechol, 3-methylcatechol, m -cresol and o -cresol from guaiacol over a Pt 3 cluster is numerically investigated using density functional theory. Further, the kinetic parameters are obtained over a wide range of temperature, i.e. 473–673 K at an interval of 50 K. Briefly, results indicate that O─H and C─H bond scissions determine the reaction rates of ‘guaiacol to catechol’ and ‘catechol to 3-methylcatechol’ reactions with activation energies of 30.32 and 41.3 kcal mol −1 , respectively. On the other hand, C─O bond scissions determine the rates of 3-methylcatechol to m - and o -cresol production reactions, respectively. The kinetics of all reactions indicate that ln k versus 1/ T plots are linear over the entire range of temperature considered herein.

Abstraction and addition kinetics of C2H radicals with CH4, C2H6, C3H8, C2H4, and C3H6: CVT/SCT/ISPE and hybrid meta-DFT methods

2015 ◽  
Vol 17 (5) ◽  
pp. 3142-3156 ◽  
Author(s):  
Manas Ranjan Dash ◽  
B. Rajakumar
Keyword(s):  
Density Functional ◽  
Transition State Theory ◽  
State Theory ◽  
Rate Coefficients ◽  
Dft Methods ◽  
Functional Theory ◽  
Variational Transition State Theory ◽  
Wide Range ◽  
P Rate ◽  
Kinetics Of

Rate coefficients for the reactions of C2H radicals with methane (k1), ethane (k2), propane (k3), ethylene (k4), and propylene (k5) were computed using canonical variational transition state theory (CVT) coupled with hybrid-meta density functional theory (DFT) over a wide range of temperatures from 150 to 5000 K.

scholarly journals Thermal Stability and Decomposition Kinetics of 1-Alkyl-2,3-Dimethylimidazolium Nitrate Ionic Liquids: TGA and DFT Study

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2560
Author(s):  
Jianwen Meng ◽  
Yong Pan ◽  
Fan Yang ◽  
Yanjun Wang ◽  
Zhongyu Zheng ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Density Functional Theory ◽  
Ionic Liquids ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Nitrogen Atmosphere ◽  
Decomposition Kinetics ◽  
Heating Rates ◽  
Functional Theory ◽  
Kinetics Of

The thermal stability and decomposition kinetics analysis of 1-alkyl-2,3-dimethylimidazole nitrate ionic liquids with different alkyl chains (ethyl, butyl, hexyl, octyl and decyl) were investigated by using isothermal and nonisothermal thermogravimetric analysis combined with thermoanalytical kinetics calculations (Kissinger, Friedman and Flynn-Wall-Ozawa) and density functional theory (DFT) calculations. Isothermal experiments were performed in a nitrogen atmosphere at 240, 250, 260 and 270 °C. In addition, the nonisothermal experiments were carried out in nitrogen and air atmospheres from 30 to 600 °C with heating rates of 5, 10, 15, 20 and 25 °C/min. The results of two heating modes, three activation energy calculations and density functional theory calculations consistently showed that the thermal stability of 1-alkyl-2,3-dimethylimidazolium nitrate ionic liquids decreases with the increasing length of the alkyl chain of the substituent on the cation, and then the thermal hazard increases. This study could provide some guidance for the safety design and use of imidazolium nitrate ionic liquids for engineering.

scholarly journals A machine learning platform for the discovery of materials

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Carl E. Belle ◽  
Vural Aksakalli ◽  
Salvy P. Russo
Keyword(s):  
Machine Learning ◽  
Density Functional ◽  
Gw Approximation ◽  
Dft Methods ◽  
Functional Theory ◽  
Unit Cell Size ◽  
Learning Platform ◽  
Photovoltaic Materials ◽  
Wide Range ◽  
Quantum Espresso

AbstractFor photovoltaic materials, properties such as band gap $$E_{g}$$ E g are critical indicators of the material’s suitability to perform a desired function. Calculating $$E_{g}$$ E g is often performed using Density Functional Theory (DFT) methods, although more accurate calculation are performed using methods such as the GW approximation. DFT software often used to compute electronic properties includes applications such as VASP, CRYSTAL, CASTEP or Quantum Espresso. Depending on the unit cell size and symmetry of the material, these calculations can be computationally expensive. In this study, we present a new machine learning platform for the accurate prediction of properties such as $$E_{g}$$ E g of a wide range of materials.

scholarly journals Analysis of the structural and electronic properties of 1-(5-Hydroxymethyl - 4 –[ 5 – (5-oxo-5-piperidin-1-yl-penta- 1,3dienyl)-benzo[1,3]dioxol-2-yl] -tetrahydro-furan-2-yl)-5- methyl-1H-pyrimidine-2,4dione molecule

2018 ◽  
Vol 33 (1) ◽  
pp. 71
Author(s):  
Ali Hashem Essa ◽  
A. F. Jalbout
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Ground State ◽  
Density Functional ◽  
Molecular Orbital Calculations ◽  
Active Molecule ◽  
Dft Methods ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Semi Empirical

The structural and electronic properties of 1-(5-Hydroxymethyl - 4 –[ 5 – (5-oxo-5-piperidin- 1 -yl-penta- 1,3 -dienyl)-benzo [1,3] dioxol- 2 -yl]- tetrahydro -furan-2 -yl)-5-methy l-1Hpyrimidine-2,4dione (AHE) molecule have been investigated theoretically by performing density functional theory (DFT), and semi empirical molecular orbital calculations. The geometry of the molecule is optimized at the level of Austin Model 1 (AM1), and the electronic properties and relative energies of the molecules have been calculated by density functional theory in the ground state. The resultant dipole moment of the AHE molecule is about 2.6 and 2.3 Debyes by AM1 and DFT methods respectively, This property of AHE makes it an active molecule with its environment, that is AHE molecule may interacts with its environment strongly in solution.

Hexaethyl-2,4-dicarba-nido-hexaborane(8), Deprotonation and Complexation Studied by NMR Spectroscopy and Density Functional Theory (DFT) Calculations

2004 ◽  
Vol 59 (6) ◽  
pp. 685-691 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Jörg Schanz
Keyword(s):  
Density Functional Theory ◽  
Nmr Spectroscopy ◽  
Density Functional ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Analogous Reaction ◽  
Sandwich Complex ◽  
Dft Methods ◽  
Functional Theory ◽  
Nmr Data

Deprotonation of hexaethyl-2,4-dicarba-nido-borane(8) 2 leads first to the hexaethyl-2,4-dicarbanido- borate(1−) 3, and further deprotonation, using BuLi/KOtBu, gives the hexaethyl-2,4-dicarbanido- hexaborate(2−) 4. The reaction of 3 with FeCl2 affords the commo-ferracarborane [Fe(Et6-2,4- C2B4H)2] 5, and the analogous reaction of 4 leads to the anionic sandwich complex [Fe(Et6-2,4- C2B4)2]2− 6 which can be protonated to give 5. The complex 5 contains two hydrido ligands, each bridging the iron and two boron atoms. Reactions were monitored and the products were characterised by 11B NMR spectroscopy in solution. The geometries of the carboranes, the borates (all unsubstituted and permethyl-substituted) and the iron complexes (all unsubstituted) were optimised by DFT methods [B3LYP/6-311+G(d,p) or B3LYP/6-31+G(d)], and the relevant NMR data [chemical shifts δ11B, δ13C, δ57Fe, and coupling constants 1J(13C,1H), 1J(11B,1H), 1J(57Fe,1H), 1J(57Fe,11B)] were calculated at the same level of theory.

scholarly journals Proposed Mechanism for the High-Yield Polymerization of Oxyethyl Propiolates with Rh Complex Catalyst Using the Density Functional Theory Method

Polymers ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 93 ◽  
Author(s):  
Yoshiaki Yoshida ◽  
Yasuteru Mawatari ◽  
Masayoshi Tabata
Keyword(s):  
Density Functional ◽  
Density Functional Theory Method ◽  
High Reactivity ◽  
High Yield ◽  
Complex Catalyst ◽  
Dft Methods ◽  
Functional Theory ◽  
Molecular Weights ◽  
Monomer Structure ◽  
The Density Functional Theory

In this study, poly(oxyethyl propiolate)s (POP)s featuring various oxyethylene derivatives are synthesized using a [Rh(norbornadiene)Cl]2 catalyst. In particular, POPs featuring the normal oxyethylene chain in the side-chain exhibit excellent yields and high molecular weights in methanol and N,N-dimethylformamide at 40 °C, compared with poly(n-alkyl propiolate)s (PnAP)s. The high reactivity of the oxyethyl propiolate (OP) monomers is clarified by considering the time dependences of the polymerization yields of OPs and alkyl propiolates (Aps). Furthermore, the monomer structure and intermediate conformation of the Rh complex are optimized using Density Function theory (DFT) methods (B3LYP/6-31G** and B3LYP/LANL2DZ) and a polymerization mechanism is proposed.

scholarly journals UV–Vis Absorption Properties of New Aromatic Imines and Their Compositions with Poly({4,8-bis[(2-Ethylhexyl)oxy]Benzo[1,2-b:4,5-b′]Dithiophene-2,6-diyl}{3-Fluoro-2-[(2-Ethylhexyl)Carbonyl]Thieno[3,4-b]Thiophenediyl})

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4191 ◽  
Author(s):  
Agnieszka Gonciarz ◽  
Robert Pich ◽  
Krzysztof Artur Bogdanowicz ◽  
Beata Jewloszewicz ◽  
Wojciech Przybył ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Organic Solar Cells ◽  
Density Functional ◽  
Bulk Heterojunction ◽  
Theoretical Calculations ◽  
Dft Methods ◽  
Functional Theory ◽  
Chemical Structures ◽  
Vis Spectroscopy ◽  
Aromatic Imines

In this paper, four new aromatic imines containing at least one thiazole-based heterocycle were analyzed in detail by UV–Vis spectroscopy, taking into consideration their chemical structures and interactions with PTB7, a known polymeric electron donor widely used in bulk heterojunction organic solar cells. It is demonstrated that the absorption spectra of the investigated active compositions can be modified not only by changing the chemical structure of imine, but also via formulations with PTB7. For all investigated imines and PTB7:imine compositions, calibration curves were obtained in order to find the optimum concentration in the composition with PTB7 for expansion and optimization of absorption spectra. All imines and PTB7:imine compositions were investigated in 1,2-dichlorobenzene by UV–Vis spectroscopy in various concentrations, monitoring the changes in the π–π* and n–π* transitions. With increasing imine concentrations, we did not observe changes in absorption maxima, while with increasing imine concentrations, a hypochromic effect was observed. Finally, we could conclude that all investigated compositions exhibited wide absorptions of up to 800 nm and isosbestic points in the range of 440–540 nm, confirming changes in the macromolecular organization of the tested compounds. The theoretical calculations of their vibration spectra (FTIR) and LUMO–HOMO levels by Density Functional Theory (DFT) methods are also provided. Finally, IR thermal images were measured for organic devices based on imines and the imine:PTB7 composite.

Comparative DFT study for molecular geometries and spectra of methyl pheophorbides-a: test of M06-2X and two other functionals

2010 ◽  
Vol 14 (07) ◽  
pp. 592-604 ◽  
Author(s):  
Do Sung Huh ◽  
Sang Joon Choe
Keyword(s):  
Density Functional Theory ◽  
Standard Deviation ◽  
Density Functional ◽  
Visible Spectrum ◽  
Mean Value ◽  
Time Dependent ◽  
Dft Methods ◽  
Functional Theory ◽  
Td Dft ◽  
The Mean

The recent interest in the application of density functional theory (DFT) has prompted us to test several functions in molecular geometries of methyl pheophorbides-a (MPa), an important starting material in photodynamic therapy (PDT). In this study, we report on tests for three popular DFT methods: M06-2X, B3LYP, and LSDA. Based on the standard deviation and the mean value, and by using the difference between optimized calculated value and experimental value in geometries, we drew the following conclusions: M06-2X/6-311+G(d,p) attained the smallest standard deviation of difference among the tested DFT methods in terms of bond length, whereas the standard deviation of bond angle in LSDA/6-311+G(d,p) was the smallest. In terms of absolute value, the mean value of LSDA/6-311+G(d,p) calculation was larger than that of M06-2X/6-311+G(d,p). We found that M06-2X/6-311+G(d,p) gave the best performance for MPa in the molecular geometries. The UV-visible spectrum was calculated with time-dependent density-functional theory (TD-DFT). Time-dependent M06-2X/6-311+G(d,p) gave the best performance for MPa in CH2Cl2 solution. In general, TD-DFT calculations in CH2Cl2 solution were more red-shifted compared with those in the solid state.

Theoretical elucidation of the energy conversion rate in organic photovoltaic cells of the fullerene nanostructure derivatives. A density functional theory study

2020 ◽  
Vol 19 (07) ◽  
pp. 2050025
Author(s):  
Nadjet Deddouche ◽  
Hafida Chemouri
Keyword(s):  
Density Functional Theory ◽  
Conversion Rate ◽  
Density Functional ◽  
Lithium Ion ◽  
Photovoltaic Cell ◽  
Energy Difference ◽  
Organic Photovoltaic ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Kinetics Of

A comparative theoretical study of the kinetics of the Diels–Alder (DA) reaction between empty fullerene (C[Formula: see text]) and lithium ion encapsulated fullerene ([Formula: see text]) with 1,3 cyclohexadiene (C[Formula: see text]H[Formula: see text]) was carried out. This reaction takes place in a photovoltaic cell. The effect of the encapsulated [Formula: see text] ion on the conversion rate of solar energy into electricity has been highlighted through calculations based on the density functional theory (DFT). In addition, a static study using the global conceptual DFT indices, as part of the demonstration of the significant electrophilic power of the fullerene nanostructure, was carried out to show the effect of encapsulating the [Formula: see text] ion in this nanoparticle on the electrophilic power of Li[Formula: see text]@C[Formula: see text] and therefore on the acceleration of the reaction. The relationship between the HOMOdonor–LUMOacceptor energy difference and the DA reaction acceleration, and therefore the acceleration of light conversion (a rapid conversion implies a small gap), has been thoroughly examined. Moreover, a mechanistic study of the kinetics of the DA reaction of the fullerene involved in an organic photovoltaic cell has been carried out. In this section, a concerted synchronous mechanism with no effect of [Formula: see text] encapsulation on the synchronicity of the reaction was observed. Finally, it was revealed that Li[Formula: see text]@C[Formula: see text] reacted approximately 2466 times faster than C[Formula: see text]. Moreover, the experimental results were found in good agreement with the computer calculations.

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