scholarly journals Spirooxazine Photoisomerization and Relaxation in Polymer Matrices

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Maria Larkowska ◽  
Michael Wuebbenhorst ◽  
Stanislaw Kucharski
Keyword(s):  
Activation Energy ◽  
Photochemical Reaction ◽  
Arrhenius Plot ◽  
Thermal Relaxation ◽  
Rheological Behaviour ◽  
Kinetic Studies ◽  
Polymer Matrices ◽  
Butyl Methacrylate ◽  
Photochromic Transformations ◽  
Uv Lamp

9′-Hydroxy-1,3,3-trimethylspiro[indoline-2,3′[3H]naphtha[2,1-b]-1,4oxazine] (SPO-7OH) was used in studies of photochromic transformations in polymer matrices. Illumination with UV lamp caused opening the spirostructure of the oxazine with formation of open merocyanine species absorbing at ca. 610 nm. The kinetic studies of thermal relaxation of the open form showed that this process can be described with a biexponential function including both photochemical reaction and rheological behaviour of the polymeric environment. Basing on Arrhenius plot of the rate constant ascribed to the photochemical reaction, the activation energy was determined, which was 66.1 and 84.7 kJ/mole for poly(methyl methacrylate-co-butyl methacrylate) and poly(vinylpyrrolidone) matrix, respectively.

ON THE DIELECTRIC BEHAVIOR OF LiCo3/5Fe2/5VO4 CERAMICS

2010 ◽  
Vol 24 (07) ◽  
pp. 665-670
Author(s):  
MOTI RAM
Keyword(s):  
Activation Energy ◽  
Dielectric Constant ◽  
Frequency Dependence ◽  
Chemical Method ◽  
Arrhenius Plot ◽  
Dielectric Behavior ◽  
Tangent Loss ◽  
Low Frequencies ◽  
Different Temperatures ◽  
Tan Δ

The LiCo 3/5 Fe 2/5 VO 4 ceramics has been fabricated by solution-based chemical method. Frequency dependence of the dielectric constant (εr) at different temperatures exhibits a dispersive behavior at low frequencies. Temperature dependence of εr at different frequencies indicates the dielectric anomalies in εr at Tc (transition temperature) = 190°C, 223°C, 263°C and 283°C with (εr) max ~ 5370, 1976, 690 and 429 for 1, 10, 50 and 100 kHz, respectively. Frequency dependence of tangent loss ( tan δ) at different temperatures indicates the presence of dielectric relaxation in the material. The value of activation energy estimated from the Arrhenius plot of log (τd) with 103/T is ~(0.396 ± 0.012) eV.

scholarly journals Polycarbonate Microchip Containing CuBTC-Monopol Monolith for Solid-Phase Extraction of Dyes

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Eman Alzahrani
Keyword(s):  
Solid Phase Extraction ◽  
Solid Phase ◽  
Solvent System ◽  
Butyl Methacrylate ◽  
Phase Extraction ◽  
Ethanolic Solution ◽  
Toxic Dyes ◽  
Relative Standard ◽  
Uv Lamp ◽  
Dye Extraction

In the present study, preparation of CuBTC-monopol monoliths for use within the microchip solid phase extraction was undertaken through a 20-min UV lamp-assisted polymerization for 2,2-dimethoxy-2-phenyl acetophenone (DMPA), butyl methacrylate (BMA), and ethylene dimethacrylate (EDMA) alongside inclusion of the porogenic solvent system (1-propanol and methanol (1 : 1)). The resultant coating underwent coating using CuBTC nanocrystals in ethanolic solution of ethanolic solution of 1,3,5-benzenetricarboxylic acid (H3BTC, 10 mM) and 10 mM copper(II) acetate Cu(CH3COO)2. This paper reports enhanced extraction, characterization, and synthesis studies for porous CuBTC metal organic frameworks that are marked by different methods including SEM/EDAX analysis, atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FT-IR). The evaluation of the microchip’s performance was undertaken as sorbent through retrieval of six toxic dyes (anionic and cationic dyes). Various parameters (desorption and extraction step flow rates, volume of desorption solvent, volume of sample, and type of desorption solvent) were examined to optimize dye extraction using fabricated microchips. The result indicated that CuBTC-monopol monoliths were permeable with the ability of removing impurities and attained high toxic dye extraction recovery (83.4–99.9%). The assessment of reproducibility for chip-to-chip was undertaken by computing the relative standard deviations (RSDs) of the six dyes in extraction. The interbatch and intrabatch RSDs ranged between 3.8 and 6.9% and 2.3 and 4.8%. Such features showed that fabricated CuBTC-monopol monolithic disk polycarbonate microchips have the potential of extracting toxic dyes that could be utilized for treating wastewater.

pH-Driven Conformational Switching of Quinoxaline Cavitands in Polymer Matrices

Synlett ◽  
2018 ◽  
Vol 29 (19) ◽  
pp. 2503-2508 ◽  
Author(s):  
E. Dalcanale ◽  
M. Torelli ◽  
I. Domenichelli ◽  
A. Pedrini ◽  
F. Guagnini ◽  
...  
Keyword(s):  
Solid State ◽  
Polymer Matrices ◽  
Switching Behavior ◽  
Butyl Methacrylate ◽  
Conformational Switching ◽  
Conformational Studies ◽  
New Class ◽  
Solid Matrices ◽  
Linear Poly ◽  
Polymeric Structures

While pH-driven interconversion of tetraquinoxaline cavitands (QxCav) from vase to kite conformation has been extensively studied both in solution and at interfaces, cavitands behavior in solid matrices is still unexplored. Therefore, the synthesis of a new class of quinoxaline cavitand based copolymers is here reported; a soluble linear poly(butyl methacrylate) (PBMA) and an insoluble cross-linked polydimethylsiloxane (PDMS), ensuring a convenient incorporation of the switchable unit, were chosen as polymer matrices. Conformational studies, performed both in solution and at the solid state, confirmed the retention of vase → kite switching behavior when moving from monomeric units to polymeric structures.

scholarly journals Pyrolysis Kinetic Parameters of Omari Oil Shale Using Thermogravimetric Analysis

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4060
Author(s):  
Ziad Abu El-Rub ◽  
Joanna Kujawa ◽  
Samer Al-Gharabli
Keyword(s):  
Activation Energy ◽  
Thermogravimetric Analysis ◽  
Kinetic Parameters ◽  
Oil Shale ◽  
Arrhenius Plot ◽  
Frequency Factor ◽  
Coefficient Of Determination ◽  
Assay Method ◽  
Temperature Integral ◽  
Integral Approximation

Oil shale is one of the alternative energies and fuel solutions in Jordan because of the scarcity of conventional sources, such as petroleum, coal, and gas. Oil from oil shale reservoirs can be produced commercially by pyrolysis technology. To optimize the process, mechanisms and rates of reactions need to be investigated. Omari oil shale formation in Jordan was selected as a case study, for which no kinetic models are available in the literature. Oil shale was analyzed using the Fischer assay method, proximate analysis (moisture, volatile, and ash), gross calorific value, elemental analysis (CHNS), and X-ray fluorescence (XRF) measurements. Non-isothermal thermogravimetric analysis was applied to study the kinetic parameters (activation energy and frequency factor) at four selected heating rates (5, 10, 15, and 20 °C/min). When oil shale was heated from room temperature to 1100 °C, the weight loss profile exhibited three different zones: drying (devolatilization), pyrolysis, and mineral decomposition. For each zone, the kinetic parameters were calculated using three selected methods: integral, temperature integral approximation, and direct Arrhenius plot. Furthermore, the activation energy in the pyrolysis zone was 112–116 kJ/mol, while the frequency factor was 2.0 × 107 − 1.5 × 109 min−1. Moreover, the heating rate has a directly proportional relationship with the rate constant at each zone. The three different methods gave comparable results for the kinetic parameters with a higher coefficient of determination (R2) for the integral and temperature integral approximation compared with the direct Arrhenius plot. The determined kinetic parameters for Omari formation can be employed in developing pyrolysis reactor models.

Kinetic Studies on the Synthesis of Hydroxyapatite Nanowires by Solvothermal Methods

2007 ◽  
Vol 60 (2) ◽  
pp. 99 ◽  
Author(s):  
Shiying Zhang ◽  
Chen Lai ◽  
Kun Wei ◽  
Yingjun Wang
Keyword(s):  
Activation Energy ◽  
Reaction Rate ◽  
Kinetic Studies ◽  
Axial Ratio ◽  
Reaction Rate Constant ◽  
Rate Equations ◽  
Solvothermal Reaction ◽  
Growth Order ◽  
Constant Diffusion ◽  
Solvothermal Methods

Hydroxyapatite nanowires with a high axial ratio have been synthesized in reverse micelle solutions that consist of cetyltrimethylammonium bromide (CTAB), n-pentanol, cyclohexane, and the reactant solution by solvothermal methods. This paper focusses on the kinetic studies of the solvothermal reaction and the linear growth of hydroxyapatite nanowires. When the reaction was carried out at low temperatures (65°C), the experimental results showed that the reaction rate was of zero order since the whole reaction was diffusion controlled with constant diffusion coefficients. In the middle to high temperature range (130–200°C), the kinetics were characterized by second order reaction kinetics. Since the controlling factor was activation energy and the apparent activation energy was large, the reaction rate was more sensitive to the temperature. Therefore, the exponent of the reaction rate constant increased by two when the temperature was increased from 130 to 200°C. By calculating the yields of products and the specific surface areas at different times, the linear and overall growth rate equations of the hydroxyapatite nanowires could be obtained. The experimental effective growth order of the crystals was 11. The larger growth order indicated that the crystal could grow more effectively in one direction because of the induction of the surfactant in the experiment system.

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

1999 ◽  
Vol 14 (9) ◽  
pp. 3552-3558 ◽  
Author(s):  
P. Torri
Keyword(s):  
Activation Energy ◽  
Water Vapor ◽  
Oxidation Resistance ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Single Layer ◽  
Water Vapor Atmosphere ◽  
Oxidation Properties ◽  
Sputter Deposited ◽  
Sic Coatings

Oxidation of sputter-deposited nanocrystalline Mo–Si–N (MoSi2.2N2.5) coatings in oxygen–water vapor atmosphere has been studied in the temperature range 400–850 °C. In addition, the oxidation properties of nanolayered Mo–Si–N/SiC coatings at 700 °C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo–Si–N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 109 (1015 atoms/cm2)2/h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo–Si–N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.

Synthetic and kinetic studies of the reversible addition of a bridging NSN fragment to the electron-rich heterocycles (R2PN)(SN)2 (R = Me, Ph, F)

1984 ◽  
Vol 62 (4) ◽  
pp. 712-715 ◽  
Author(s):  
Neil Burford ◽  
Tristram Chivers ◽  
Richard T. Oakley ◽  
Tom Oswald
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Nmr Spectroscopy ◽  
Kinetic Studies ◽  
Reductive Elimination ◽  
Membered Ring ◽  
High Yield ◽  
Kinetic Measurements ◽  
Bicyclic Compounds ◽  
Reversible Addition

The oxidative addition of Cl2 (using SO2Cl2) to the six-membered ring (R2PN)(SN)2 (R = Me, Ph) produces the mixed phosphazene–thiazyl heterocycles, (R2PN)(NSCl)2, which react with Me3SiNSNSiMe3 to give the bicyclic compounds R2PS3N5. The latter undergo thermal decomposition, at ca. 100 °C in toluene, via reductive elimination of an NSN unit to regenerate (R2PN)(SN)2 in high yield. Kinetic measurements of this process, using 31P nmr spectroscopy, yield an activation energy of 102.4 ± 6.0 kJ mol−1 for the release of the NSN fragment from Me2PS3N5. The thermolysis route has been used to prepare the thermally unstable (F2PN)(SN)2, characterized as a 1:1 adduct with norbornadiene.

The Effects of Doping and Temperature on the Fermi Level and its Relationship to the Recrystallization Growth Velocity in Ion-Implanted Silicon

1988 ◽  
Vol 100 ◽  
Author(s):  
L. E. Mosley ◽  
M. A. Paesler ◽  
P. D. Richard
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Growth Rate ◽  
Fermi Level ◽  
Growth Velocity ◽  
Growth Process ◽  
Arrhenius Plot ◽  
Velocity Versus ◽  
Band Bending ◽  
P Type

ABSTRACTIt has been observed that doping produces an enhancement in the recrystallization growth rate of silicon made amorphous by ionimplantation. This enhancement has been attributed to a shift of the Fermi level with doping. Evidence supporting this is based on the compensating effect of implantation of n- and p-type dopants together. We have previously proposed a model of the recrystallization growth process based on the diffusion of dangling bonds. We suggested that the rate enhancement is due to band bending at the amorphous-crystalline interface produced by doping. We have calculated the change in activation energy for the recrystallization growth velocity for a number of doping concentrations as a function of temperature. The major contribution to the apparent lowering of the activation energy with doping in an Arrhenius plot of the growth velocity versus I/kT is due to the temperature dependence of the Fermi level. Experimental data are compared with the calculated results. In addition differences in the measured growth rates in thermal and laser annealed samples are discussed, with primary emphasis on the lack of a change in the activation energy with doping in the laser annealed case.

Direct observation of dienols produced by photochemical enolisation of α,β-unsaturated ketones: rates and activation parameters for dienol reketonisation via a 1,5-hydrogen shift

1987 ◽  
Vol 65 (8) ◽  
pp. 1867-1872 ◽  
Author(s):  
Randy M. Duhaime ◽  
Alan C. Weedon
Keyword(s):  
Activation Energy ◽  
Low Temperatures ◽  
Nmr Spectra ◽  
Arrhenius Plot ◽  
Activation Parameters ◽  
Activation Entropy ◽  
Hydrogen Shift ◽  
Unsaturated Ketones ◽  
Ultraviolet Light Irradiation ◽  
Stable Solutions

The production of stable solutions of Z-dienols by ultraviolet light irradiation of α,β-unsaturated ketones at low temperatures (ca. −76 °C) in d4-methanol is reported. The rates of reketonisation of the dienols via a 1,5-sigmatropic hydrogen shift were determined at various temperatures between −43 °C and + 2 °C by monitoring the proton nmr spectra of the dienols. From the data the activation parameters for the reaction were calculated. For the dienol Z-2-hydroxy-4-methyl-2,4-pentadiene, 2, derived from photoenolisation of 4-methyl-3-penten-2-one, 1, the activation energy from the Arrhenius plot is 62 ± 4 kJ/mol, and the activation entropy and enthalpy from the Eyring plot are −87 ± 15 J/mol K and 60 ± 4 kJ/mol, respectively. For the dienol Z-4-tert-butyl-2-hydroxy-2,4-pentadiene, 4, obtained from photoenolisation of 4,5,5-trimethyl-3-hexen-2-one, 3, the activation energy, entropy, and enthalpy were found to be 47 ± 5 kJ/mol, −135 ± 19 J/mol K, and 45 ± 5 kJ/mol, respectively.

Impurity Conduction in Silicon Carbide

2007 ◽  
Vol 556-557 ◽  
pp. 367-370 ◽  
Author(s):  
Michael Krieger ◽  
Kurt Semmelroth ◽  
Heiko B. Weber ◽  
Gerhard Pensl ◽  
Martin Rambach ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Low Temperatures ◽  
Nearest Neighbor ◽  
Arrhenius Plot ◽  
Schottky Contacts ◽  
Steep Slope ◽  
Admittance Spectroscopy ◽  
Resistivity Measurements ◽  
Impurity Conduction

We report on admittance spectroscopy (AS) investigations taken on aluminum (Al)- doped 6H-SiC crystals at low temperatures. Admittance spectra taken on Schottky contacts of highly doped samples (NA ≥ 7.2×1017 cm-3) reveal two series of conductance peaks, which cause two different slopes of the Arrhenius plot. The steep slope is attributed to the Al acceptor, while the flatter one - obtained from the low temperature peaks - is attributed to the activation energy ε3 of nearest neighbor hopping. We propose a model, which explains the unexpected sharpness of the low temperature conductance peaks and the disappearance of these peaks for low acceptor concentrations. The model is verified by simulation, and the AS results are compared with corresponding results obtained from resistivity measurements taken on 4H- and the identical 6HSiC samples.

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