scholarly journals Structure, density and viscosity of water

2021 ◽  
pp. 96-105
Author(s):  
V.G. Nefedov ◽  
◽  
V.V. Matveev
Keyword(s):  
Water Clusters ◽  
Dispersion Interactions ◽  
First Case ◽  
Temperature Dependences ◽  
Arrhenius Temperature Dependence ◽  
Experimental Activation Energy ◽  
Structure Density ◽  
Ice Floes ◽  
Arrhenius Temperature ◽  
Volumetric Content

We analyzed the possibilities of the use of the cluster model of water to assess its viscosity. The Nemethy-Scheraga model was used in our study. In a simplified version, this model implies the presence of water cluster that are linked by hydrogen bonds as well as individual molecules (monomolecules) interacting only by van der Waals forces. The paper gives an estimation of average cluster size. Based on the experimental temperature dependences of viscosity and density, the content of monomolecules in water was approximately determined. In the first case, the ratio of the viscosity of water to monomolecules was estimated from the inverse Arrhenius temperature dependence of viscosity by considering experimental activation energy ~18.6 kJ mol–1 (0÷300C) and energy of dispersion interactions ~7.4 kJ mol–1. Then, the volumetric content of monomolecules was estimated by using the inverse Betchelor's formula, which relates the viscosity of the suspension (clusters) and dispersion medium (monomolecules) to their ratio. On the other hand, a similar estimation was performed based on the density of water, clusters that were considered similar to ice floes, and the estimated density of monomolecules. Both estimates showed that the volumetric content of water not bound into clusters does not exceed 9%. It was concluded that the structure of water most likely corresponds to the clathrate model, according to which some of the H2O molecules move into the middle of ice-like clusters, and vacancies are stabilized by H3O+–OH– pairs.

scholarly journals Unentangled Vitrimer Melts: Interplay between Chain Relaxation and Cross-link Exchange Controls Linear Rheology

2020 ◽  
Author(s):  
RALM RICARTE ◽  
Sachin Shanbhag
Keyword(s):  
Activation Energy ◽  
A Priori ◽  
Relaxation Times ◽  
Cross Link ◽  
Time Dynamics ◽  
Temperature Dependences ◽  
Long Time ◽  
Arrhenius Temperature Dependence ◽  
Short Time ◽  
Arrhenius Temperature

<div>Using this theoretical approach, we explore the influence of molecular structure and temperature on vitrimer linear</div><div>viscoelasticity. We observe that vitrimers with uniform and random cross-link distributions exhibit larger viscosities</div><div>and relaxation times than gradient and blocky types. Polydimethylsiloxane vitrimer (which has a flexible backbone) shows an Arrhenius temperature dependence for viscosity, while polystyrene vitrimers (which has rigid backbones) are only Arrhenius at high temperatures. During stress relaxation, the short time dynamics represent monomer friction, while the long time dynamics encompass a combination of network strand relaxation and cross-link exchange. Because of the different temperature dependences of the processes, time-temperature superposition fails. We also show that the effective rheological activation energy can be estimated a priori using only the cross-link exchange activation energy and the backbone Williams-Landel-Ferry parameters.</div><div><br></div><div>(Submitted to Macromolecules)</div>

scholarly journals Unentangled Vitrimer Melts: Interplay between Chain Relaxation and Cross-link Exchange Controls Linear Rheology

2021 ◽  
Author(s):  
RALM RICARTE ◽  
Sachin Shanbhag
Keyword(s):  
Activation Energy ◽  
A Priori ◽  
Relaxation Times ◽  
Cross Link ◽  
Time Dynamics ◽  
Temperature Dependences ◽  
Long Time ◽  
Arrhenius Temperature Dependence ◽  
Short Time ◽  
Arrhenius Temperature

<div>Using this theoretical approach, we explore the influence of molecular structure and temperature on vitrimer linear viscoelasticity. We observe that vitrimers with uniform and random cross-link distributions exhibit larger viscosities and relaxation times than gradient and blocky types. Polydimethylsiloxane vitrimer (which has a flexible backbone) shows an Arrhenius temperature dependence for viscosity, while polystyrene vitrimers (which has rigid backbones) are only Arrhenius at high temperatures. During stress relaxation, the short time dynamics represent monomer friction, while the long time dynamics encompass a combination of network strand relaxation and cross-link exchange. Because of the different temperature dependences of the processes, time-temperature superposition fails. We also show that the effective rheological activation energy can be estimated a priori using only the cross-link exchange activation energy and the backbone Williams-Landel-Ferry parameters.</div><div><br></div><div>(Submitted to Macromolecules)</div>

scholarly journals Unentangled Vitrimer Melts: Interplay between Chain Relaxation and Cross-link Exchange Controls Linear Rheology

2020 ◽  
Author(s):  
RALM RICARTE ◽  
Sachin Shanbhag
Keyword(s):  
Activation Energy ◽  
A Priori ◽  
Relaxation Times ◽  
Cross Link ◽  
Time Dynamics ◽  
Temperature Dependences ◽  
Long Time ◽  
Arrhenius Temperature Dependence ◽  
Short Time ◽  
Arrhenius Temperature

<div>Using this theoretical approach, we explore the influence of molecular structure and temperature on vitrimer linear</div><div>viscoelasticity. We observe that vitrimers with uniform and random cross-link distributions exhibit larger viscosities</div><div>and relaxation times than gradient and blocky types. Polydimethylsiloxane vitrimer (which has a flexible backbone) shows an Arrhenius temperature dependence for viscosity, while polystyrene vitrimers (which has rigid backbones) are only Arrhenius at high temperatures. During stress relaxation, the short time dynamics represent monomer friction, while the long time dynamics encompass a combination of network strand relaxation and cross-link exchange. Because of the different temperature dependences of the processes, time-temperature superposition fails. We also show that the effective rheological activation energy can be estimated a priori using only the cross-link exchange activation energy and the backbone Williams-Landel-Ferry parameters.</div><div><br></div><div>(Submitted to Macromolecules)</div>

Self-diffusion of Ag+ and Na+ in molten Ca(NO3)2-KNO3

1972 ◽  
Vol 25 (8) ◽  
pp. 1613 ◽  
Author(s):  
BJ Welch ◽  
CA Angell
Keyword(s):  
Electrical Conductance ◽  
Ionic Species ◽  
Tracer Diffusion ◽  
Dilute Solution ◽  
Self Diffusion ◽  
Capillary Method ◽  
Arrhenius Temperature Dependence ◽  
Radio Tracer ◽  
Tracer Diffusion Coefficients ◽  
Arrhenius Temperature

In order to explore the behaviour of diffusing ionic species in a molten salt in which non-Arrhenius behaviour of other transport properties is established, the diffusivities in dilute solution of Ag+ and Na+ in 38.1 mol% Ca(NO3)2+ 61.9 mol% KNO3 have been measured. For both ions limited radio-tracer diffusion coefficients, determined using a diffusion-out-of-capillary method, are reported. D(Ag+) has also been measured by chronopotentiometry, by which means the range and reliability of the measurements were considerably extended. Chronopotentiometric and tracer data agree within expected errors of measurement. Both ionic diffusivities show a non-Arrhenius temperature dependence which is indistinguishable in magnitude from that of the electrical conductance of the solvent melt.

scholarly journals DC conductivity of polyethylene and crosslinked polyethylene measured with a dynamic temperature program

2017 ◽  
Author(s):  
Hossein Ghorbani ◽  
Carl-Olof Olsson ◽  
Marc Jeroense
Keyword(s):  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Thermal Conditions ◽  
Dc Conductivity ◽  
Protective Film ◽  
Dynamic Temperature ◽  
Operation Conditions ◽  
Heating And Cooling ◽  
Arrhenius Temperature Dependence ◽  
Arrhenius Temperature

<p>Electrical conductivity of HVDC cable insulation materials is important for its function. It is very practical to evaluate this parameter by DC conductivity measurements on press molded polymeric plates samples. While in real operation conditions, the insulation undergoes both static and dynamic thermal conditions, most of the published research in this area is still focused only on steady state thermal conditions. In this work, the focus is instead on the behavior of electrical conductivity under dynamic thermal conditions. Press molded XLPE and LDPE plate samples with different preparations are tested under 25 kV/mm DC field with a dynamic temperature profile ranging from room temperature to 90 °C.<br />It was discovered that in many cases, the measured conductivity during dynamic measurements strongly deviates from the expected Arrhenius temperature dependence; instead the conductivity shows a nonmonotonic<br />temperature dependence manifested as conductivity peaks during heating and cooling. The behavior is found to be strongly related to the type of protective film used during press molding of the sample; further degassing leads to a reduction of the nonmonotonic temperature dependence and with long<br />degassing the behavior tends to the expected Arrhenius temperature dependence.</p>

scholarly journals Intrinsic electrical properties of cable bacteria reveal an Arrhenius temperature dependence

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Robin Bonné ◽  
Ji-Ling Hou ◽  
Jeroen Hustings ◽  
Koen Wouters ◽  
Mathijs Meert ◽  
...  
Keyword(s):  
Electron Transport ◽  
Electrical Properties ◽  
Temperature Dependence ◽  
Electrical Characterization ◽  
Electrical Circuit ◽  
Parallel Fibre ◽  
Thermally Activated ◽  
Arrhenius Temperature Dependence ◽  
Equivalent Electrical Circuit Model ◽  
Arrhenius Temperature

AbstractFilamentous cable bacteria exhibit long-range electron transport over centimetre-scale distances, which takes place in a parallel fibre structure with high electrical conductivity. Still, the underlying electron transport mechanism remains undisclosed. Here we determine the intrinsic electrical properties of the conductive fibres in cable bacteria from a material science perspective. Impedance spectroscopy provides an equivalent electrical circuit model, which demonstrates that dry cable bacteria filaments function as resistive biological wires. Temperature-dependent electrical characterization reveals that the conductivity can be described with an Arrhenius-type relation over a broad temperature range (− 195 °C to + 50 °C), demonstrating that charge transport is thermally activated with a low activation energy of 40–50 meV. Furthermore, when cable bacterium filaments are utilized as the channel in a field-effect transistor, they show n-type transport suggesting that electrons are the charge carriers. Electron mobility values are ~ 0.1 cm2/Vs at room temperature and display a similar Arrhenius temperature dependence as conductivity. Overall, our results demonstrate that the intrinsic electrical properties of the conductive fibres in cable bacteria are comparable to synthetic organic semiconductor materials, and so they offer promising perspectives for both fundamental studies of biological electron transport as well as applications in microbial electrochemical technologies and bioelectronics.

scholarly journals Vitrification decoupling from α-relaxation in a metallic glass

2020 ◽  
Vol 6 (17) ◽  
pp. eaay1454
Author(s):  
Xavier Monnier ◽  
Daniele Cangialosi ◽  
Beatrice Ruta ◽  
Ralf Busch ◽  
Isabella Gallino
Keyword(s):  
Metallic Glass ◽  
Temperature Dependence ◽  
Metallic Glasses ◽  
Materials Science ◽  
Scanning Calorimetry ◽  
Fictive Temperature ◽  
Fundamental Properties ◽  
Fast Scanning Calorimetry ◽  
Arrhenius Temperature Dependence ◽  
Arrhenius Temperature

Understanding how glasses form, the so-called vitrification, remains a major challenge in materials science. Here, we study vitrification kinetics, in terms of the limiting fictive temperature, and atomic mobility related to the α-relaxation of an Au-based bulk metallic glass former by fast scanning calorimetry. We show that the time scale of the α-relaxation exhibits super-Arrhenius temperature dependence typical of fragile liquids. In contrast, vitrification kinetics displays milder temperature dependence at moderate undercooling, and thereby, vitrification takes place at temperatures lower than those associated to the α-relaxation. This finding challenges the paradigmatic view based on a one-to-one correlation between vitrification, leading to the glass transition, and the α-relaxation. We provide arguments that at moderate to deep undercooling, other atomic motions, which are not involved in the α-relaxation and that originate from the heterogeneous dynamics in metallic glasses, contribute to vitrification. Implications from the viewpoint of glasses fundamental properties are discussed.

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