Studies of Polymer Solvation by Dielectric Relaxation Spectroscopy IV:Polyvinylpyrrolidone in Urea Derivatives at Different Temperatures

1991 ◽  
Vol 46 (11) ◽  
pp. 1001-1008 ◽  
Author(s):  
M. Rohmann ◽  
M. Stockhausen
Keyword(s):  
Activation Enthalpy ◽  
Repeat Unit ◽  
Dielectric Spectrum ◽  
Type Ii ◽  
Polymer Content ◽  
Dielectric Relaxation Spectroscopy ◽  
Urea Derivatives ◽  
Solvation Numbers ◽  
Different Temperatures ◽  
Repeat Unit Of Polymer

AbstractThe dielectric spectrum is measured up to 72 GHz of solutions of polyvinylpyrrolidone (PVP) in tetramethylurea (TMU), dimethylethylene urea and dimethylpropylene urea. Concentrations are up to a monomole fraction of 0.65 (PVP 1200) or 0.5 (PVP 40 000). Measuring temperatures are 20CC for all systems and additionally 40 and 60°C for the TMU solutions. For the description of the results a superposition of Debye type components is used, which are discussed in particular with respect to the solvent contributions. These can be distinguished into three regions: (i) Unaffected bulk-type; (ii) loosely affected, relaxation time and activation enthalpy increasing with increasing polymer content; (iii) quasi bound and moving together with the polymer. The solvation numbers (total of affected solvent per repeat unit of polymer) are about 1.5 to 2.

Kinetic Studies on the Polymerization of Dicyclohexylmethylmethane-4,4'-Diisocyanate with Polyoxytetramethylene Diol

2013 ◽  
Vol 791-793 ◽  
pp. 32-35
Author(s):  
Jian Cheng Wang
Keyword(s):  
Rate Constant ◽  
Arrhenius Equation ◽  
Activation Enthalpy ◽  
Kinetic Studies ◽  
Activation Entropy ◽  
Dimethyl Acetamide ◽  
Different Temperatures ◽  
Ft Ir ◽  
Temperature Activation

Dicyclohexylmethylmethane-4,4'-diisocyanate is used to react with polyoxytetramethylene diol at different temperatures. N,N-Dimethyl acetamide is used as solvent.In situFT-IR is used to monitor the reaction to work out rate constant, Arrhenius equation and Eyring equation. The polymerization has been found to be a second order reaction, and the rate constant increases with the rise of temperature. Activation energy (Ea), activation enthalpy (ΔH) and activation entropy (ΔS) for the polymerization are respectively calculated out, which are very useful to reveal the reaction mechanism.

scholarly journals Influence of macroclumping on type II supernova light curves

2019 ◽  
Vol 629 ◽  
pp. A17
Author(s):  
Luc Dessart ◽  
Edouard Audit
Keyword(s):  
Light Curve ◽  
Early Time ◽  
Radiation Energy ◽  
Mean Free Path ◽  
Light Curves ◽  
Type Ii ◽  
Different Temperatures ◽  
Curve Modeling ◽  
2D And 3D ◽  
The Impact

Core-collapse supernova (SN) ejecta are probably structured on both small and large scales, with greater deviations from spherical symmetry nearer the explosion site. Here, we present 2D and 3D gray radiation hydrodynamics simulations of type II SN light curves from red and blue supergiant star explosions to investigate the impact of inhomogeneities in density or composition on SN observables, with a characteristic scale set to a few percent of the local radius. Clumping is found to hasten the release of stored radiation, boosting the early time luminosity and shortening the photospheric phase. Around the photosphere, radiation leaks between the clumps where the photon mean free path is greater. Since radiation is stored uniformly in volume, a greater clumping can increase this leakage by storing more and more mass into smaller and denser clumps containing less and less radiation energy. An inhomogeneous medium in which different regions recombine at different temperatures can also impact the light curve. Clumping can thus be a source of diversity in SN brightness. Clumping may lead to a systematic underestimate of ejecta masses from light curve modeling, although a significant offset seems to require a large density contrast of a few tens between clumps and interclump medium.

The hydrolyses of some sterically crowded benzoate esters in sulfuric acid. The excess acidity method at different temperatures

1979 ◽  
Vol 57 (22) ◽  
pp. 2960-2966 ◽  
Author(s):  
Robin A. Cox ◽  
Malcolm F. Goldman ◽  
Keith Yates
Keyword(s):  
Sulfuric Acid ◽  
Activation Enthalpy ◽  
Sulfuric Acid Concentration ◽  
Hydrolysis Rate ◽  
Water Molecules ◽  
Steric Strain ◽  
Methyl Substitution ◽  
Different Temperatures ◽  
Acid Catalyzed ◽  
Aqueous Standard

The excess acidity method has been used to analyze the observed acid-catalyzed hydrolysis rate constants for methyl benzoate, methyl para-toluate, methyl ortho-toluate, and methyl 2,6-dimethylbenzoate, over a wide sulfuric acid concentration range, at several different temperatures. Enthalpies and entropies of activation in the aqueous standard state are reported, with slope parameters m≠ also given are the [Formula: see text] and m* values found for the protonation of these compounds. The mechanistic changeover from AAc-2 to AAc-1 hydrolysis occurs at lower acidity with increasing methyl substitution, mainly due to the decrease in activation enthalpy in the transition state for the AAc-1 process, caused by release of steric strain and increased mesomeric interaction. The AAc-2 hydrolysis involves two water molecules, and is energetically favourable and entropically unfavourable. The AAc-1 reaction is difficult energetically, but this is offset by the large positive activation entropies found.

A New Model for Predicting Sorption Isotherm of Water in Foods

2011 ◽  
Vol 7 (2) ◽  
Author(s):  
Farid B. Cortés ◽  
Farid Chejne ◽  
Benjamin Rojano
Keyword(s):  
Sorption Isotherms ◽  
Isosteric Heat ◽  
Type Ii ◽  
Experimental Isotherm ◽  
New Model ◽  
Operation Costs ◽  
Theoretical Predictions ◽  
Different Temperatures ◽  
Total Experimental Time ◽  
Using Data

A new model for predicting sorption isotherms of type II and III based on the Polanyi theory is proposed. This model allows the prediction of the sorption isotherms at different temperatures from one experimental isotherm. The theoretical predictions of isotherms and isosteric heat were validated successfully using data from literature for twenty one foods. This method allows total experimental time and operation costs to be reduced.

scholarly journals Thermodynamics of the DNA Repair Process by Endonuclease VIII

Acta Naturae ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 29-37 ◽  
Author(s):  
O. A. Kladova ◽  
N. A. Kuznetsov ◽  
O. S. Fedorova
Keyword(s):  
Activation Enthalpy ◽  
Substrate Binding ◽  
Repair Process ◽  
Molecular Processes ◽  
Substrate Interaction ◽  
Enzyme Substrate ◽  
Different Temperatures ◽  
Enthalpy And Entropy ◽  
Transition Complex ◽  
Dna Substrate

In the present work, a thermodynamic analysis of the interaction between endonuclease VIII (Endo VIII) and model DNA substrates containing damaged nucleotides, such as 5,6-dihydrouridine and 2-hydroxymethyl-3-hydroxytetrahydrofuran (F-site), was performed. The changes in the fluorescence intensity of the 1,3-diaza-2-oxophenoxazine (tCO) residue located in the complementary chain opposite to the specific site were recorded in the course of the enzyme-substrate interaction. The kinetics was analyzed by the stopped-flow method at different temperatures. The changes of standard Gibbs free energy, enthalpy, and entropy of sequential steps of DNA substrate binding, as well as activation enthalpy and entropy for the transition complex formation of the catalytic stage, were calculated. The comparison of the kinetic and thermodynamic data characterizing the conformational transitions of enzyme and DNA in the course of their interaction made it possible to specify the nature of the molecular processes occurring at the stages of substrate binding, recognition of the damaged base, and its removal from DNA.

Effects of ionized impurity and interface roughness scatterings on the electron mobility in InAs/GaSb type II superlattices at low temperatures

2016 ◽  
Vol 30 (32n33) ◽  
pp. 1650384
Author(s):  
S. Safa ◽  
A. Asgari
Keyword(s):  
Electron Mobility ◽  
Low Temperatures ◽  
Structural Parameters ◽  
Impurity Scattering ◽  
Interface Roughness ◽  
Type Ii ◽  
Type Ii Superlattices ◽  
Interface Roughness Scattering ◽  
Different Temperatures ◽  
Scattering Rates

The in-plane electron mobility has been calculated in InAs/GaSb type-II superlattices (SLs) at low temperatures. The interface roughness scattering and ionized impurity scattering are investigated as the dominant scattering mechanisms in limiting the electron transport at low temperatures. For this purpose, the band structures and wave functions of electrons in such SLs are calculated by solving the K.P Hamiltonian using the numerical Finite Difference method. The scattering rates have been obtained for different temperatures and structural parameters. We show that the scattering rates are high in thin-layer SLs and the mobility rises as the temperature increases in low-temperature regime.

Melting of mixtures in silica nanopores

2009 ◽  
Vol 81 (10) ◽  
pp. 1953-1959 ◽  
Author(s):  
Joanna Czwartos ◽  
Malgorzata Sliwinska-Bartkowiak ◽  
Benoit Coasne ◽  
Keith E. Gubbins
Keyword(s):  
Phase Diagram ◽  
Carbon Fibers ◽  
Pore Diameter ◽  
Nanoporous Materials ◽  
Experimental Measurements ◽  
Activated Carbon Fibers ◽  
Dielectric Relaxation Spectroscopy ◽  
Average Pore ◽  
Different Temperatures ◽  
Solid Liquid

We report experimental measurements of the melting of mixtures confined in nanoporous materials. Dielectric relaxation spectroscopy (DRS) was used to determine the solid–liquid phase diagram of bromobenzene/carbon tetrachloride (C6H5Br /CCl4) mixtures confined in controlled pore glasses (CPGs) with an average pore diameter H = 7.5 nm. Our results show that the phase diagram of the confined mixture is of the same type as that for the bulk, but the solid–liquid coexistence lines are located at different temperatures. These results are compared with those previously obtained for CCl4/C6H6 mixtures in activated carbon fibers (ACFs).

scholarly journals Temperature dependence of the microwave dielectric properties of $$\gamma$$-aminobutyric acid

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jie Hou ◽  
Sisay Mebre Abie ◽  
Runar Strand-Amundsen ◽  
Yuri M. Galperin ◽  
Joakim Bergli ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Dielectric Properties ◽  
Neuronal Excitability ◽  
Sudden Change ◽  
Microwave Dielectric Properties ◽  
Solution Viscosity ◽  
Gamma Aminobutyric Acid ◽  
Dielectric Relaxation Spectroscopy ◽  
Inhibitory Neurotransmitter ◽  
Different Temperatures

AbstractThe GABA molecule is the major inhibitory neurotransmitter in the mammalian central nervous system. Through binding to post-synaptic neurons, GABA reduces the neuronal excitability by hyperpolarization. Correct binding between the GABA molecules and its receptors relies on molecular recognition. Earlier studies suggest that recognition is determined by the geometries of the molecule and its receptor. We employed dielectric relaxation spectroscopy (DRS) to study the conformation and dielectric properties of the GABA molecule under physiologically relevant laboratory conditions. The dielectric properties of GABA investigated have given us new insights about the GABA molecule, such as how they interact with each other and with water molecules at different temperatures (22°C and 37.5°C). Higher temperature leads to lower viscosity, thus lower relaxation time. The change in the GABA relaxation time due to concentration change is more associated with the solution viscosity than with the GABA dipole moment. A resonance behavior was observed with high GABA concentrations at physiological temperature, where there might be a phase transition at a certain temperature for a given GABA concentration that leads to a sudden change of the dielectric properties.

The Effect of Temperature Elevation on Microwave-Transmitting Property of Organosilicone-Matrix Radome

2016 ◽  
Vol 848 ◽  
pp. 174-178
Author(s):  
Qian Wang
Keyword(s):  
High Temperature ◽  
Theoretical Model ◽  
Operating Temperature ◽  
Dielectric Spectrum ◽  
Effect Of Temperature ◽  
Matrix Composites ◽  
Temperature Elevation ◽  
Gradient Distribution ◽  
Spectrum Measurement ◽  
Different Temperatures

In this paper, both the permittivity and the microwave transmittance properties of organosilicon-matrix composites under different temperatures have been studied. In order to investigate the reason for the changing of dielectric property, both TGA and high-temperature dielectric spectrum measurement have been carried out. A theoretical model of radome, with a temperature gradient distribution, has been built to analyze the dependence of microwave transmittance property on temperature. Based on the experimental results, we can optimize the effective operating temperature of this kind of organosilicone-matrix composites.

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