Viscosity calculations at molecular dynamics simulations

Kirova, E M; Norman, G. É.

doi:10.1088/1742-6596/653/1/012106

Cited by 39 publications

(34 citation statements)

References 10 publications

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“…Molecular dynamics simulations coupled with the pioneering Green-Kubo method [4,5], appear to be efficient at low viscosity values and ambient conditions [6,7]. This method uses internal equilibrium fluctuations, by evaluating integrals of autocorrelation functions, to describe transport properties such as zero shear (low shear) viscosity.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Mathas

Holweger

Wolf

et al. 2021

Tribology Transactions

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The behavior of lubricants at operational conditions, such as at high pressures, is a topic of great industrial interest. In particular, viscosity and the viscosity-pressure relation are especially important for applications and their determination by computational simulations is very desirable. In this study we evaluate methods to compute these quantities based on fully atomistic molecular dynamics simulations which are computationally demanding but also have the potential to be most accurate. We used the 9,10dimethyloctadecane molecule, main component of PAO-2 base oil as the lubricant for our tests. The methods used for the viscosity simulations are the Green-Kubo equilibrium molecular dynamics (EMD-GK) and non-equilibrium molecular dynamics (NEMD), at pressures of up to 1.0 GPa and various temperatures (40-150 degrees Celsius). We present the theory behind these methods and investigate how the simulation parameters affect the results obtained, to ensure viscosity convergence with respect to the A c c e p t e d M a n u s c r i p t simulation intervals and all other parameters. We show that by using each method in its regime of applicability, we can achieve good agreement between simulated and measured values. NEMD simulations at high pressures captured zero shear viscosity successfully, while at 40 degrees Celsius EMD-GK is only applicable to pressures up to 0.3 GPa, where the viscosity is lower. In NEMD, longer and multiply repeated simulations improve the confidence interval of viscosity, which is essential at lower pressures. Another aspect of these methods is the choice of the utilized force field for the atomic interactions. This was investigated by selecting two different commonly used force fields.

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Section: Introductionmentioning

confidence: 99%

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Mathas

Holweger

Wolf

et al. 2021

Tribology Transactions

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“…Other transport properties, such as self‐diffusion (velocity auto‐correlation), [ 109 ] viscosity (pressure tensor auto‐correlation), [ 110 ] and thermal conductivity (heat flux auto‐correlation), [ 111 ] can also be obtained from these simulations using Green‐Kubo relations.…”

Section: Thermodynamic Properties Obtained From Dftmentioning

confidence: 99%

Experimental methods in chemical engineering: Density functional theory

et al. 2021

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Density functional theory (DFT) computations apply to physics, chemistry, material science, and engineering. In chemical engineering, DFT identifies material structure and properties, and mechanisms for phenomena such as chemical reaction and phase transformation that are otherwise impossible to measure experimentally. Even though its practical application dates back only a decade or two, it is already a standard tool for materials modelling. Many textbooks and articles describe the theoretical basis of DFT, but it remains difficult for researchers to autonomously learn the steps to accurately calculate system properties. Here, we first explain the foundations of DFT in a way accessible to chemical engineers with little background in quantum mechanics or solid‐state physics. Then, we introduce the basics of the computations and, for most of the rest of the article, we show how to derive physical characteristics of interest to chemical engineers: elastic, thermodynamic, and surface properties, electronic structure, and surface and chemical reaction energy. Finally, we highlight some limitations of DFT; since these calculations are approximations to the Schrödinger equation, their accuracy relies on choosing adequate exchange‐correlation functions and basis sets. Since 1991, the number of articles WoS has indexed related to DFT has increased quadratically with respect to time and now numbers 15 000. A bibliometric analysis of the top 10 000 cited articles in 2018 and 2019 classifies them into four clusters: adsorption, graphene, and nanoparticles; ab initio molecular dynamics and crystal structure; electronic structure and optical properties; and total energy calculations and wave basis sets.

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“…[89,90] Molecular simulations have also been performed to predict diffusion coefficient of polymer solutions. [89,[91][92][93] For further detailed information on diffusion of polymer solutions and modeling, the reader is referred to the works from Refs. [60,[84][85][86][87][88][94][95][96][97], since this subject will not be the further focus of this Review.…”

Section: From Viscosity To Diffusivitymentioning

confidence: 99%

“…[105] In EMD, typically the shear viscosity computed using the Green-Kubo or the Einstein-Helfand relations. [92,101] In NEMD simulations, a perturbation is applied to the fluid system and the shear viscosity is estimated from the resulting steady states or time-transient behavior. [106] Several authors have used molecular simulations to study the properties of diluted and semi dilute polymer solutions under shear flow.…”

Section: Molecular Simulationsmentioning

confidence: 99%

State‐Of‐The‐Art Quantification of Polymer Solution Viscosity for Plastic Waste Recycling

et al. 2021

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Solvent-based recycling is a promising approach for closed-loop recovery of plastic-containing waste. It avoids the energy cost to depolymerize the plastic but still allows to clean the polymer of contaminants and additives. However, viscosity plays an important role in handling the polymer solutions at high concentrations and in the cleaning steps. This Review addresses the viscosity behavior of polymer solutions, available data, and (mostly algebraic) models developed. The non-Newtonian viscosity models, such as the Carreau and Yasuda-Cohen-Armstrong models, pragmatically describe the viscosity of polymer solutions at different concentrations and shear rate ranges. This Review also describes how viscosity influences filtration and centrifugation processes, which are crucial steps in the cleaning of the polymer and includes a polystyrene/ styrene case study.

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Viscosity calculations at molecular dynamics simulations

Cited by 39 publications

References 10 publications

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Experimental methods in chemical engineering: Density functional theory

State‐Of‐The‐Art Quantification of Polymer Solution Viscosity for Plastic Waste Recycling

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