Quantitative study of diffusion jumps in atomistic simulations of model gas–polymer systems

Raptis, T. E.; Raptis, Vasilios; Samios, Jannis

doi:10.1080/00268976.2012.663511

Cited by 18 publications

(29 citation statements)

References 31 publications

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“…The position of the molecule at the l th time step is r l ( t ; t *), while r CM ( t ; t *) is the center of the trajectory segment. The distance traveled by a molecule λ j ( t , t *) during the j th trajectory segment is calculated using the following equation. − …”

Section: Methods and Modelsmentioning

confidence: 99%

Breakdown of the Stokes–Einstein Relation in Supercooled Water/Methanol Binary Mixtures: Explanation Using the Translational Jump-Diffusion Approach

Dubey

Daschakraborty

2020

J. Phys. Chem. B

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A recent experiment has directly checked the validity of the Stokes−Einstein (SE) relation for pure water, pure methanol, and their binary mixtures of three different compositions at different temperatures. The effect of composition on the nature of breakdown of the SE relation is interesting. While in the majority of the systems, an increasing SE breakdown is observed with decreasing temperature, the breakdown is already significant at higher temperatures for the equimolar mixture. Violations of the SE relation in pure supercooled water at different temperatures and pressures have been previously explained using the translational jump-diffusion (TJD) approach, which provides a fundamental molecular basis, by directly connecting the SE breakdown with jump-diffusion of the molecules. We have used the same TJD approach for explaining the SE breakdown for the methanol/water binary mixtures of compositions studied in the experiment over a wide range of temperatures between 220 K and 300 K. We have understood that the jump-diffusion is the key responsible factor for the SE breakdown. The maximum jump-diffusion contribution gives rise to the early SE breakdown observed for the equimolar mixture observed in the experiment. This study, therefore, provides molecular insight into the SE breakdown for the supercooled water/methanol binary mixture, as found in the experiment.

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Section: Methods and Modelsmentioning

confidence: 99%

Breakdown of the Stokes–Einstein Relation in Supercooled Water/Methanol Binary Mixtures: Explanation Using the Translational Jump-Diffusion Approach

Dubey

Daschakraborty

2020

J. Phys. Chem. B

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“…The distance traversed by the molecule in a trajectory segment λ(t) can be calculated from the formula, . [39][40][41] We note that the translational jump occurrences are not ubiquitous in all these trajectory segments. At this point, we need an efficient method in order to correctly identify the translational jump segments.…”

Section: Figure 2amentioning

confidence: 99%

“…deviates from the Gaussianity ( ) [40,41] at the most at time t * . Both the and are plotted in Figure 2b for T=210 K and in Figure S2 of the SM for the rest of the temperatures.…”

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confidence: 99%

Decoupling of Translational Diffusion from the Viscosity of Supercooled Water: Role of Translational Jump Diffusion

2019

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Some experiments have witnessed increasing decoupling of viscosity from the translational self-diffusion of supercooled water with decreasing temperature. While theory and computer simulation studies indicated the jump translation of the molecules as a probable origin of the above decoupling, a precise quantitative estimation is still lacking. Through a molecular dynamics (MD) simulation study, along with careful consideration of translational jump motion, we have found the most definite proof of increasing relevance of translational jump diffusion in the above decoupling phenomena. By separating out the jump-only diffusion contribution from the overall diffusion of the water, we obtain the residual diffusion coefficient, which remains strongly coupled with the viscosity of the medium at the whole temperature range, including supercooled regime. These new findings can help to elucidate many experimental studies featuring molecular transport properties, where strong diffusion-viscosity decoupling comes into the picture. 3There are intriguing properties of supercooled water, including a strong decoupling between its viscosity and the diffusion of the molecules. Some experimental studies [1][2][3] -including that by Dehaoui et al.[4]-has revealed an increasing decoupling of viscosity from the water translational diffusion coefficient upon cooling. This indicates a gradual breakdown of the Stokes-Einstein (SE) relation ( with decreasing temperature. In contrast, the rotational diffusion D r remains coupled with for a wide range of temperature, which implies the validity of the Stokes-Einstein-Debye (SED) relation. Similar decoupling between D t and  was alsoreported earlier in other molecular glass forming liquids.[5-13] The SE relation is obeyed at sufficiently high temperature, but severely breaks down around 1.3T g (T g is the glass transition temperature). On the contrary, the rotational diffusion of the molecular glass forming liquid and the medium viscosity remain hydrodynamically coupled even at the temperature very close to T g .Deeply supercooled liquids have spatially heterogeneous dynamics, which have been confirmed by various experiments (e.g., see Refs. 5,6,[14][15][16][17] and computer simulation studies (e.g., see . A number of computer simulation studies have indicated that the emerging spatiotemporal heterogeneity in supercooled water and other supercooled liquids has connection with the increasing violation of the SE relation with decreasing temperature. [23][24][25][26][27][28][29][30] Recently, two of us have shown that the rotation assisted translational movement of solvent water around a nonpolar solute induces translational jump-diffusion of a tracer from one solvent cage to another in supercooled water.[23]Even though the prior studies have implied the pivotal role of translational jumpdiffusion for the breakdown of the SE relation in supercooled water, a quantitative estimation of the explicit contribution of the jump-only diffusion D Jump (diffusion due to jump only motion) is still missing...

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“…The Molecular Dynamics (MD) method [ 31 , 32 , 33 , 34 ] was used to simulate the diffusion process of gases in PVDF. The diffusion cell of PVDF and CH 4 /CO 2 /H 2 S gas mixture molecules was constructed with the Amorphous Cell module.…”

Section: Model and Simulation Methodologymentioning

confidence: 99%

Molecular Simulation on Permeation Behavior of CH4/CO2/H2S Mixture Gas in PVDF at Service Conditions

Zhang

Chu

et al. 2022

Polymers

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Reinforced thermoplastic composite pipes (RTPs) have been widely used for oil and gas gathering and transportation. Polyvinylidene fluoride (PVDF) has the greatest potential as a thermoplastic liner of RTPs due to its excellent thermal and mechanical properties. However, permeation of gases is inevitable in the thermoplastic liner, which may lead to blister failure of the liner and damage the safe operation of the RTPs. In order to clarify the permeation behavior and obtain the permeation mechanism of the mixture gas (CH4/CO2/H2S) in PVDF at the normal service conditions, molecular simulations were carried out by combining the Grand Canonical Monte Carlo (GCMC) method and the Molecular Dynamics (MD) method. The simulated results showed that the solubility coefficients of gases increased with the decrease in temperature and the increase in pressure. The adsorption isotherms of all gases were consistent with the Langmuir model. The order of the adsorption concentration for different gases was H2S > CO2> CH4. The isosteric heats of gases at all the actual service conditions were much less than 42 kJ/mol, which indicated that the adsorption for all the gases belonged to the physical adsorption. Both of the diffusion and permeation coefficients increased with the increase in temperature and pressure. The diffusion belonged to Einstein diffusion and the diffusion coefficients of each gas followed the order of CH4 > CO2 > H2S. During the permeation process, the adsorption of gas molecules in PVDF exhibited selective aggregation, and most of them were adsorbed in the low potential energy region of PVDF cell. The mixed-gas molecules vibrated within the hole of PVDF at relatively low temperature and pressure. As the temperature and pressure increase, the gas molecules jumped into the neighboring holes occasionally and then dwelled in the holes, moving around their equilibrium positions.

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Quantitative study of diffusion jumps in atomistic simulations of model gas–polymer systems

Cited by 18 publications

References 31 publications

Breakdown of the Stokes–Einstein Relation in Supercooled Water/Methanol Binary Mixtures: Explanation Using the Translational Jump-Diffusion Approach

Breakdown of the Stokes–Einstein Relation in Supercooled Water/Methanol Binary Mixtures: Explanation Using the Translational Jump-Diffusion Approach

Decoupling of Translational Diffusion from the Viscosity of Supercooled Water: Role of Translational Jump Diffusion

Molecular Simulation on Permeation Behavior of CH4/CO2/H2S Mixture Gas in PVDF at Service Conditions

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