The description of the change in characteristic temperatures of thermomechanical and viscoelastic properties of polymers and elastomers with deformation frequency or of temperature dependence of polymer p
The description of the change in characteristic temperatures of thermomechanical and viscoelastic properties of polymers and elastomers with deformation frequency or of temperature dependence of polymer properties is widely achieved by two equations: (1) the Williams‐Landel‐Ferry (WLF) equation and (2) the Arrhenius equation. Mostly the WLF equation is used. Often the distinction between the two descriptions is based on the argument: if volume processes play the key role, then WLF equation is the right one, if thermally activated processes play the key role, then Arrhenius equation is the right one. Both equations are based on the activation of processes, and always the temperature is the variable, which activate the processes. Both descriptions are methods to parameterize the temperature dependence of properties or the change of characteristic temperatures, as glass‐rubber transition temperature, with deformation rate. Also, the so‐called ‘volume processes’ are controlled by temperature, but the thermal activation can be small in energy to initiate the change in spatial position from one site to another for a molecule. This means both descriptions should be congruent. In this article, the congruence is shown and the relation between WLF parameters and Arrhenius parameters will be established. For this, a slight modification of the usual Arrhenius equation is necessary. Also, other descriptions are discussed in short: Doolittle equation and Vogel‐Fulcher equation, they were or are used to describe the change of viscosity with temperature in melts or solutions.
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Electrical conductivities of pure tetraalkylammonium-(N+Me4, N+Et4, N+Bu4, N(+)Me(3)Hex) and imida-zolium- (EMIM+, BMIM+) based ionic liquids (ILs) with bis(trifluoromethylsulfonyl) imide (TFSI-) anion and their acetonitrile solut...
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Electrical conductivities of pure tetraalkylammonium-(N+Me4, N+Et4, N+Bu4, N(+)Me(3)Hex) and imida-zolium- (EMIM+, BMIM+) based ionic liquids (ILs) with bis(trifluoromethylsulfonyl) imide (TFSI-) anion and their acetonitrile solutions were measured in two temperature ranges of 298-368 and 298-348 K. Acetonitrile was used as an organic solvent to decrease the viscosity of ILs and, therefore, to increase the mobility of charge carriers. The maximum conductivity of acetonitrile solutions of both tetraalkylammonium- and imidazolium-based ILs was found to decrease with cation size. The conductivity - temperature dependencies of pure ILs and their acetonitrile solutions were analyzed using three approaches based on the Arrhenius equation for non-associating electrolytes, the Vogel-Fulcher-Tammann equation for ionic conductivity of glass-forming liquids and the Litovitz equation for associated liquids. The dilution of ILs with acetonitrile significantly reduced their activation energies of conductivity. At the same time, the activation energy decreased with increasing the alkyl chain length because of the deceleration of the ion transfer and the growth of the viscosity. (C) 2018 Elsevier Ltd. All rights reserved.
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A solid solution of lead-free piezoelectric ceramic (1-x)Bi-0.50(Na0.80K0.20)(0.50)TiO3-xBa(0.90)Ca(0.10)-Ti0.90Zr0.10O3 (with x = 0.00, 0.02, 0.04, 0.06, 0.08) was synthesized by conventional solid-state reaction route. The effec...
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A solid solution of lead-free piezoelectric ceramic (1-x)Bi-0.50(Na0.80K0.20)(0.50)TiO3-xBa(0.90)Ca(0.10)-Ti0.90Zr0.10O3 (with x = 0.00, 0.02, 0.04, 0.06, 0.08) was synthesized by conventional solid-state reaction route. The effect of addition of BCZT on BNKT was investigated on structural, microstructural, dielectric, ferroelectric, piezoelectric and high-density energy storage properties experimentally. Modified Curie Weiss law and Vogel-Fulcher law were employed to study the diffusivity and activation energy. The dielectric dispersion with frequency reveals the relaxor behavior for all compositions. The value of T-v (calculated from Vogel-Fulcher relation) decreases while the corresponding value of Ea increases with the BCZT composition. The unipolar curve shows the increased strain of 0.15% and corresponding d*33 (S-max/E-max = 311 pm/V) for x = 0.02 composition among all studied compositions. Furthermore, compositions x = 0.02 and x = 0.04 shows the improved energy storage efficiency similar to 50% with respect to pure BNKT. (c) 2018 Elsevier B.V. All rights reserved.
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In this work, two pyrrolidonium based ionic liquids namely N-methyl pyrrolidonium bisulfate ([NMP][HSO4]) and pyrrolidonium bisulfate ([PY][HSO4]) were synthesized and characterized by H-1 NMR spectroscopy technique. The experimen...
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In this work, two pyrrolidonium based ionic liquids namely N-methyl pyrrolidonium bisulfate ([NMP][HSO4]) and pyrrolidonium bisulfate ([PY][HSO4]) were synthesized and characterized by H-1 NMR spectroscopy technique. The experimental density, speed of sound, viscosity and conductivity have been measured in the temperature range of (293.15-333.15) K and at 0.1 MPa pressure. From the experimental data, derived thermodynamic properties such as molecular volume, standard entropy, crystal energy, isobaric expansion coefficient, molecular free length and molar conductivity have been calculated. Empirical equations, Newton-Laplace equation, Vogel-Tammann-Fulcher equation and Walden equation were presented to understand the nature of the pure ionic liquids. Further, experimental measurements for density and speed of sound of binary mixtures of [PY][HSO4] with water and/or DMSO were studied as a function of IL concentration at various temperatures and apparent molar properties were-calculated using Redlich-Mayer equation. Finally, experimental and derived thermodynamic properties were explored to understand the intermolecular interactions of studied systems. (C) 2016 Elsevier B.V. All rights reserved.
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Density, dynamic viscosity, and electrical conductivity of binary mixtures of ethaline (choline chloride + ethylene glycol at molar ratio 1:2) as a deep eutectic solvent (DES) with dimethyl sulfoxide were measured under atmospheri...
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Density, dynamic viscosity, and electrical conductivity of binary mixtures of ethaline (choline chloride + ethylene glycol at molar ratio 1:2) as a deep eutectic solvent (DES) with dimethyl sulfoxide were measured under atmospheric pressure at temperatures, T, from (308.15 to 363.15) K covering the entire mixture range. The mixtures exhibited negative excess molar volumes, V-E, with a minimum at ethaline mole fractions of x(1) approximate to 0.4...0.5 that became more pronounced with increasing temperature. A similar minimum was found for the excess viscosity, Delta eta, of the mixtures. However, in contrast to V-E the minimum of Delta eta became more shallow with increasing T. As expected, the electrical conductivity of the mixtures increased monotonically with increasing x(1) and T. The temperature dependence of viscosity and conductivity is well described by the Vogel-Fulcher-Tamman (VFT) equation. (C) 2016 Elsevier B.V. All rights reserved.
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In this work, ionic conductivity data as a function of temperature in the pyridinium-based ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-2-methylpyridinium tetrafluoroborate, 1-butyl-3-meth...
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In this work, ionic conductivity data as a function of temperature in the pyridinium-based ionic liquids 1-butylpyridinium tetrafluoroborate, 1-butylpyridinium triflate, 1-butyl-2-methylpyridinium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-butyl-4-methyIpyridinium tetrafluoroborate, 1-butyl-3-methyIpyridinium dicyanamide, and l-octyl-3-methylpyridinium tetrafluoroborate, are reported. A comparison of results for this series of ionic liquids has been used to evaluate the influence of the ionic structural characteristic in this transport property. Temperature dependence of experimental values has been fitted by means of the Vogel-Fulcher-Tammann equation, and from their parameters, maximum conductivity and activation energy for conduction have been derived. From conductivity parameters and the glass transition temperature, a detailed analysis has been performed in fragility terms. Finally, the classical Walden rule has been used to classify the ionic liquids depending on the relationship between conductivity and fluidity.
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The polycrystalline samples of (Pb_(0.90)Ba_(0.10)) [(Zn_(1/3)Nb_(2/3))_(0.20)-(Zr_(0.51)Ti_(0.49))_(0.80)]O_3 [PBZN-PZT] compositions ceramics have been synthesized by substitution of barium in PZN-PZT by precipitation method and...
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The polycrystalline samples of (Pb_(0.90)Ba_(0.10)) [(Zn_(1/3)Nb_(2/3))_(0.20)-(Zr_(0.51)Ti_(0.49))_(0.80)]O_3 [PBZN-PZT] compositions ceramics have been synthesized by substitution of barium in PZN-PZT by precipitation method and finally by modified columbite method. X-ray diffraction (XRD) analysis of (Pb_(0.90)Ba_(0.10))(Zn)(1/3)Nb)(2/3))O_3 (PBZN) and PBZN-PZT shows a cubic and mixed phase of tetragonal and rhombohedral pure perovskite structure at room temperature. The dielectric dispersion of the solid solutions of PBZN-PZT has been studied as a function of temperature for the frequency range from 100 Hz to 1 MHz. The temperature (T) variation of the real components (ε') at different frequencies of the dielectric permittivity shows a broad maximum. The diffuse peaks in permittivity versus temperature confirm the relaxor behaviour of PBZN-PZT. The frequency dependence of maximum temperature (T_m) in these compounds with barium substitution is modeled using Vogel-Fulcher relation.
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In the present work, phase transitions and electrical characteristics of iron and lanthanum substituted lead titanate are reported. Structural analysis of the prepared samples was carried out to confirm the formation of the compou...
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In the present work, phase transitions and electrical characteristics of iron and lanthanum substituted lead titanate are reported. Structural analysis of the prepared samples was carried out to confirm the formation of the compounds in the proper phase. The average grain size was estimated using Scherrer's equation. Dielectric properties of the samples have been studied as functions of temperature and frequency. Variations of the dielectric constant (ε_r) as function of temperature show a diffuse ferro-paraelectric phase transition. The diffusivity and the relaxation strength were estimated using the modified Uchino-law, and the relaxation time of these materials satisfies the Vogel-Fulcher equation.
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? 2021 Elsevier B.V.1-(2-Methoxyethyl)-3-methylimidazolium acetic acid ([C1OC2mim][OAc]), 1-(2-methoxyethyl)-3-methylimidazolium propionic acid ([C1OC2mim][Pro]) and 1-(2-ethoxyethyl)-3-methylimidazolium propionic acid ([C2OC2mim]...
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? 2021 Elsevier B.V.1-(2-Methoxyethyl)-3-methylimidazolium acetic acid ([C1OC2mim][OAc]), 1-(2-methoxyethyl)-3-methylimidazolium propionic acid ([C1OC2mim][Pro]) and 1-(2-ethoxyethyl)-3-methylimidazolium propionic acid ([C2OC2mim][Pro]) were successfully prepared by two-step synthesis method. Based on the standard addition method, the physicochemical parameters of the density, viscosity and electrical conductivity for ether-functionalized ionic liquids (ILs) were measured. The volume properties of three ether-functionalized ILs and their homologues were estimated by semi-empirical methods. According to the Eying viscosity equation, the relationship between viscosity and activation Gibbs energy for viscous flow (ΔG≠) was studied. The activation energy values for three ether-functionalized ILs were calculated by Arrhenius empirical equation. The activation energies of these ether-functionalized ILs are arranged in the following order: [C1OC2mim][Pro] (Eη = 39.17 kJ·mol?1) > [C2OC2mim][Pro] (Eη = 37.26 kJ·mol?1) > [C1OC2mim][OAc] (Eη = 37.23 kJ·mol?1). Futhermore, the Vogel-Fulcher-Tamman (VFT) equation is used to describe the relationship between viscosity (or electrical conductivity or molar electrical conductivity) and temperature, and the experimental results show that VFT equation has good general applicability.
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