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Keywords = VFT equation

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11 pages, 27459 KiB  
Article
Deep Eutectic Solvents Based on N-Methyltrifluoroacetamide and Lithium Bis(trifluoromethanesulfonyl)imide as New Electrolytes with Low Viscosity and High Ionic Conductivity
by Guihong Lyu, Carsten Korte and Jiangshui Luo
Materials 2025, 18(9), 2048; https://doi.org/10.3390/ma18092048 - 30 Apr 2025
Viewed by 682
Abstract
In this work, we present a study on the thermal/transport properties of a novel deep eutectic solvent (DES) obtained by using N-methyltrifluoroacetamide (FNMA) as the hydrogen bond donor (HBD) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the hydrogen bond acceptor (HBA). The binary phase diagram, [...] Read more.
In this work, we present a study on the thermal/transport properties of a novel deep eutectic solvent (DES) obtained by using N-methyltrifluoroacetamide (FNMA) as the hydrogen bond donor (HBD) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the hydrogen bond acceptor (HBA). The binary phase diagram, thermal stability, flammability, viscosity and ionic conductivity of the as-prepared DESs were investigated at atmospheric pressure. The binary phase diagram shows a range of eutectic molar ratios (xLiTFSI = 0.2~0.33), with the lowest deep eutectic temperature of −84 °C. At xLiTFSI = 0.2 (i.e., FNMA:LiTFSI = 4:1 and denoted as DES-4:1). The as-prepared DES composition exhibits high thermal stability (onset temperature of weight loss = 78 °C), a low viscosity (η = 48.9 mPa s at 25 °C), relatively high ionic conductivity (σ = 0.86 mS cm−1 at 25 °C) and non-flammability. The transport properties, including ionic conductivity and viscosity, as a function of temperature are in accordance with the Vogel–Fulcher–Tammann (VFT) equations. With increasing molar ratio of HBD vs. HBA, the viscosity decreases, and the ionic conductivity increases at a given temperature between 25 °C and 80 °C. The roughly equal pseudo-activation energies for ion transport and viscous flow in each composition imply a strong coupling of ion transport and viscous flow. Walden plots indicate vehicular transport as the main ion transport mechanism for the DES-4:1 and DES-3:1 compositions; meanwhile, it was confirmed that the ionic conductivity and viscous flow are strictly coupled. The present work is expected to provide strategies for the development of wide-temperature-range and safer electrolytes with low salt concentrations. Full article
(This article belongs to the Special Issue Advances in Electronic and Photonic Materials)
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16 pages, 6890 KiB  
Article
Crystallization of Zr-Based Amorphous Alloys in Laser Welding
by Shiju Yan, Chengli Song, Lingling Huang, Liang Han and Chengyong Wang
Metals 2023, 13(7), 1283; https://doi.org/10.3390/met13071283 - 17 Jul 2023
Cited by 3 | Viewed by 1439
Abstract
Crystallization often occurs in the laser welding of amorphous alloys, reducing the properties of amorphous alloys. Therefore, the research in this thesis focuses on the experimental selection of suitable welding parameters to prevent crystallization of Zr-based amorphous alloys during the laser welding process. [...] Read more.
Crystallization often occurs in the laser welding of amorphous alloys, reducing the properties of amorphous alloys. Therefore, the research in this thesis focuses on the experimental selection of suitable welding parameters to prevent crystallization of Zr-based amorphous alloys during the laser welding process. As such, it is necessary to simulate the temperature field curve of the welding area by computer and then determine the power and laser moving speed of laser welding. In this paper, the temperature field curve of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) amorphous alloy in laser welding is obtained by finite element analysis. The continuous heating curve (CHT) of Vit1 is fitted by the Vogel–Fulcher–Tammann (VFT) equation and the Kissinger equation. If the temperature field curve intersects with the CHT curve, crystallization occurs. The experiment results show that the VFT equation can be used to predict the crystallization of Vit1 better in laser welding. The temperature and welding time are increased by using a low welding speed. Therefore, the temperature of the weld zone cannot fall in time, resulting in the intersection of the temperature field curve and the CHT curve. Thus, crystallization can be avoided if the welding speed is controlled within a reasonable range, and the highest temperature is kept under the CHT curve. The combination of the CHT curve and the temperature field curve shows that the samples at 300 W-3 mm/s and 300 W-6 mm/s welding parameters all undergo crystallization, while the samples at 300 W-9 mm/s and 300 W-12 mm/s welding parameters do not undergo crystallization. Through the flexural test, it is found that the flexural strength of the welded interface is at its the maximum under 300 W-9 mm/s. Full article
(This article belongs to the Special Issue Advanced Biomedical Materials (2nd Edition))
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15 pages, 1372 KiB  
Article
Transport Properties of Protic Ionic Liquids Based on Triazolium and Imidazolium: Development of an Air-Free Conductivity Setup
by Eduardo Maurina Morais, Alexander Idström, Lars Evenäs and Anna Martinelli
Molecules 2023, 28(13), 5147; https://doi.org/10.3390/molecules28135147 - 30 Jun 2023
Cited by 6 | Viewed by 2610
Abstract
The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C2HTr124]) and the ethylimidazolium ([C2HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients [...] Read more.
The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C2HTr124]) and the ethylimidazolium ([C2HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients were measured and discussed, extending the discussion to the concept of fragility. Furthermore, in order to allow the measurement of the ionic conductivity of very small volumes (<0.5 mL) of ionic liquid under an inert and dry atmosphere, a new setup was developed. It was found that the cation nature strongly affected the transport properties, the [C2HTr124] cation resulting in slower dynamics than the [C2HIm] one. This was concluded from both conductivity and diffusivity measurements while for both properties, the anion had a lesser effect. By fitting the conductivity data with the Vogel–Fulcher–Tammann (VFT) equation, we could also estimate the fragility of these ionic liquids, which all fell in the range of very fragile glass-forming materials. Finally, the slower dynamics observed in the triazolium-based ionic liquids can be rationalized by the stronger interactions that this cation establishes with both anions, as deduced from the frequency analysis of relevant Raman signatures and density functional theory (DFT) calculations. Full article
(This article belongs to the Special Issue Properties and Applications of Ionic Liquids-Based Advanced Materials)
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18 pages, 2284 KiB  
Article
On Molecular Dynamics and Charge Transport in a Flexible Epoxy Resin Network
by Orestis Vryonis, Alun S. Vaughan, Thomas Andritsch, Peter H. F. Morshuis and Aurore Claverie
Materials 2022, 15(18), 6413; https://doi.org/10.3390/ma15186413 - 15 Sep 2022
Cited by 5 | Viewed by 1879
Abstract
An epoxy based on diglycidyl ether of bisphenol A was reacted with a long-chain poly(oxypropylene diamine) hardener in the presence of an accelerator, resulting in a flexible epoxy network. Tensile properties were tested as a function of accelerator concentration. All systems exhibited high [...] Read more.
An epoxy based on diglycidyl ether of bisphenol A was reacted with a long-chain poly(oxypropylene diamine) hardener in the presence of an accelerator, resulting in a flexible epoxy network. Tensile properties were tested as a function of accelerator concentration. All systems exhibited high levels of extensibility, with strain at failure values in excess of 65%. Molecular dynamics in a formulation containing 10 phr of accelerator were then examined using dielectric spectroscopy over the temperature range of 103–433 K. At low temperatures, a molecular relaxation process (γ relaxation) was observed and shown to conform well to both the Arrhenius equation and activated tunnelling. A stronger relaxation appeared (203–303 K) just before the onset of charge transport, which dominated the behaviour at higher temperatures. The former takes an unusual bimodal form, which we consider a result of overlapping β and α relaxations, consequently termed αβ mode. Analysis of this mechanism revealed a Vogel–Fulcher–Tammann (VFT) behaviour. The temperature-dependent DC conductivity, σDC (deduced from the low-frequency charge transport contribution to εr″), also revealed VFT behaviour with an onset statistically equivalent to that of the αβ mode, therefore suggesting that charge transport, at this temperature regime, is strongly affiliated with cooperative molecular motion. Full article
(This article belongs to the Special Issue Advances in Electric Insulating Materials and Applications)
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14 pages, 3833 KiB  
Article
Crystal Memory near Discontinuous Triacylglycerol Phase Transitions: Models, Metastable Regimes, and Critical Points
by David A. Pink, Marjorie Ladd-Parada, Alejandro G. Marangoni and Gianfranco Mazzanti
Molecules 2020, 25(23), 5631; https://doi.org/10.3390/molecules25235631 - 30 Nov 2020
Cited by 1 | Viewed by 2068
Abstract
It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been [...] Read more.
It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been detected. Solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered. We outlined a mathematical model, with a single phase transition, that shows how the time-temperature observations can be explained, makes predictions, and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of “crystal memory” and to show boundaries beyond which “crystal memory” is not observed. A plot of the lifetime of a metastable state versus temperature, using the modified VFT equation, agrees with recent time-temperature data. The model can be falsified through its predictions: the model possesses a critical point and we outline a procedure describing how it could be observed by changing the hydrocarbon chain length. We make predictions about how thermodynamic functions will change as the critical point is reached and as the system enters a crossover regime. The model predicts that the phenomenon of “crystal memory” will not be observed unless the system is cooled from a superheated metastable regime associated with a discontinuous phase transition. Full article
(This article belongs to the Special Issue Crystallization of Lipids: From Fundamentals to Applications)
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6 pages, 616 KiB  
Proceeding Paper
Thermophysical Characterization of TFSI Based Ionic Liquid and Lithium Salt Mixtures
by Lois Fernández-Miguez, Pablo Vallet, Lucia Camila Tasende-Rodríguez, Alejandro Doval, Maria Villanueva, Óscar Cabeza, Luis Miguel Varela, Josefa Salgado and Juan José Parajó
Proceedings 2019, 41(1), 57; https://doi.org/10.3390/ecsoc-23-06618 - 14 Nov 2019
Cited by 1 | Viewed by 1977
Abstract
The ionic liquids (ILs) doped with metal salts have become a real alternative as electrolytes for batteries, but the right choice of these compounds for reaching the adequate properties and performance is still a challenge, and strategies are therefore needed for achieving it. [...] Read more.
The ionic liquids (ILs) doped with metal salts have become a real alternative as electrolytes for batteries, but the right choice of these compounds for reaching the adequate properties and performance is still a challenge, and strategies are therefore needed for achieving it. The thermophysical properties of IL 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([bmpyr] [TFSI]) and its mixture with bis-(trifluoromethane)-sulfonimide lithium salt (from 0.1 m to saturation level) were determined in this work. These properties are density (ρ), speed of sound (U), and corresponding derived magnitudes, such as the bulk modulus and the thermal coefficient, as well as electrical conductivity (σ) against temperature. Density shows a linear decreasing dependence with temperature and a clear increase with the addition of salt, whereas the thermal expansion coefficient increases with temperature and salt addition. Speed of sound decreases with both temperature and salt concentration, and the adiabatic compressibility calculated by means of the well-known Laplace equation increases, as expected, with temperature in all the studied cases, although a small variation with concentration was observed. Electrical conductivity increases with temperature following the Vogel–Fulcher–Tammann (VFT) equation and decreases with the addition of salt. Full article
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8 pages, 1247 KiB  
Article
Temperature Dependence on Density, Viscosity, and Electrical Conductivity of Ionic Liquid 1-Ethyl-3-Methylimidazolium Fluoride
by Fengguo Liu, Xiongwei Zhong, Junli Xu, Ali Kamali and Zhongning Shi
Appl. Sci. 2018, 8(3), 356; https://doi.org/10.3390/app8030356 - 1 Mar 2018
Cited by 19 | Viewed by 7329
Abstract
Ionic liquids are considered environmentally friendly media for various industrial applications. Basic data on physicochemical properties are significant for a new material, in terms of developing its potential applications. In this work, 1-ethyl-3-methylimidazolium fluoride ([EMIm]F) ionic liquid was synthesized via an anion metathesis [...] Read more.
Ionic liquids are considered environmentally friendly media for various industrial applications. Basic data on physicochemical properties are significant for a new material, in terms of developing its potential applications. In this work, 1-ethyl-3-methylimidazolium fluoride ([EMIm]F) ionic liquid was synthesized via an anion metathesis process. Physical properties including the density, viscosity, electrical conductivity, and thermal stability of the product were measured. The results show that the density of [EMIm]F decreases linearly with temperature increases, while dynamic viscosity decreases rapidly below 320 K and the temperature dependence of electrical conductivity is in accordance with the VFT (Vogel–Fulcher–Tammann) equation. The temperature dependence of the density, conductivity, and viscosity of [EMIm]F can be expressed via the following equations: ρ = 1.516 − 1.22 × 10−3 T, σm = 4417.1exp[−953.17/(T − 166.65)] and η = 2.07 × 10−7exp(−5.39 × 104/T), respectively. [EMIm]F exhibited no clear melting point. However, its glass transition point and decomposition temperature are −71.3 °C and 135 °C, respectively. Full article
(This article belongs to the Section Materials Science and Engineering)
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14 pages, 10408 KiB  
Article
On the Fragility of Bulk Metallic Glass Forming Liquids
by Isabella Gallino
Entropy 2017, 19(9), 483; https://doi.org/10.3390/e19090483 - 10 Sep 2017
Cited by 37 | Viewed by 10545
Abstract
In contrast to pure metals and most non-glass forming alloys, metallic glass-formers are moderately strong liquids in terms of fragility. The notion of fragility of an undercooling liquid reflects the sensitivity of the viscosity of the liquid to temperature changes and describes the [...] Read more.
In contrast to pure metals and most non-glass forming alloys, metallic glass-formers are moderately strong liquids in terms of fragility. The notion of fragility of an undercooling liquid reflects the sensitivity of the viscosity of the liquid to temperature changes and describes the degree of departure of the liquid kinetics from the Arrhenius equation. In general, the fragility of metallic glass-formers increases with the complexity of the alloy with differences between the alloy families, e.g., Pd-based alloys being more fragile than Zr-based alloys, which are more fragile than Mg-based alloys. Here, experimental data are assessed for 15 bulk metallic glasses-formers including the novel and technologically important systems based on Ni-Cr-Nb-P-B, Fe-Mo-Ni-Cr-P-C-B, and Au-Ag-Pd-Cu-Si. The data for the equilibrium viscosity are analyzed using the Vogel–Fulcher–Tammann (VFT) equation, the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) equation, and the Adam–Gibbs approach based on specific heat capacity data. An overall larger trend of the excess specific heat for the more fragile supercooled liquids is experimentally observed than for the stronger liquids. Moreover, the stronger the glass, the higher the free enthalpy barrier to cooperative rearrangements is, suggesting the same microscopic origin and rigorously connecting the kinetic and thermodynamic aspects of fragility. Full article
(This article belongs to the Special Issue Thermodynamics in Material Science)
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17 pages, 920 KiB  
Review
Bond Strength—Coordination Number Fluctuation Model of Viscosity: An Alternative Model for the Vogel-Fulcher-Tammann Equation and an Application to Bulk Metallic Glass Forming Liquids
by Masahiro Ikeda and Masaru Aniya
Materials 2010, 3(12), 5246-5262; https://doi.org/10.3390/ma3125246 - 10 Dec 2010
Cited by 45 | Viewed by 12413
Abstract
The Vogel-Fulcher-Tammann (VFT) equation has been used extensively in the analysis of the experimental data of temperature dependence of the viscosity or of the relaxation time in various types of supercooled liquids including metallic glass forming materials. In this article, it is shown [...] Read more.
The Vogel-Fulcher-Tammann (VFT) equation has been used extensively in the analysis of the experimental data of temperature dependence of the viscosity or of the relaxation time in various types of supercooled liquids including metallic glass forming materials. In this article, it is shown that our model of viscosity, the Bond Strength—Coordination Number Fluctuation (BSCNF) model, can be used as an alternative model for the VFT equation. Using the BSCNF model, it was found that when the normalized bond strength and coordination number fluctuations of the structural units are equal, the viscosity behaviors described by both become identical. From this finding, an analytical expression that connects the parameters of the BSCNF model to the ideal glass transition temperature T0 of the VFT equation is obtained. The physical picture of the Kohlrausch-Williams-Watts relaxation function in the glass forming liquids is also discussed in terms of the cooperativity of the structural units that form the melt. An example of the application of the model is shown for metallic glass forming liquids. Full article
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