High-Frequency Shear Modulus and Relaxation Time of Soft-Sphere and Lennard–Jones Fluids

Keshavarzi, Ezat; Vahedpour, M.; Alavi, Saman; Najafi, Bijan

doi:10.1007/s10765-004-7733-6

Cited by 4 publications

(4 citation statements)

References 23 publications

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“…This results in a different time scale (τ * = 0.067) than defined by Eq. (11). We know that if linear viscoelastic theory is validṖ yx (0) =γ G ∞ and P yx (0) =γ η, where η is close to the Newtonian viscosity.…”

Section: -6mentioning

confidence: 99%

“…The viscoelastic relaxation of simple fluids has been studied by a number of authors [2,[7][8][9][10][11][12]. Mountain and Zwanzig [9] studied the density dependence of the Maxwell relaxation time of a supercritical Lennard-Jones fluid.…”

Section: Introductionmentioning

confidence: 99%

“…They found a decrease in relaxation time with increasing density up to the maximum density studied, ρ = 0.7. More recently, Keshavarzi et al [11] studied the density and temperature dependence of the infinitefrequency shear modulus and the Maxwell relaxation time for purely repulsive soft sphere and Lennard-Jones fluids. They calculated the infinite-frequency shear modulus numerically from the equilibrium radial distribution function, using the relation derived by Zwanzig and Mountain [13].…”

Section: Introductionmentioning

confidence: 99%

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Density dependence of the stress relaxation function of a simple fluid

2013

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We present accurate molecular dynamics calculations of the shear stress relaxation modulus of a simple atomic fluid over a wide range of densities. The high accuracy of the data enables us to study changes in the functional form of the shear relaxation modulus, and the properties that are derived from it, as the density is increased from the ideal gas limit to the upper limit of the fluid range. We show that the shear relaxation modulus of a dilute atomic fluid can be accurately described with a simple functional form consisting of a Gaussian plus a single exponential, whereas the dense fluid exhibits a more complicated relaxation function. The infinite-frequency shear modulus, the zero-shear viscosity, and the zero-shear first normal stress coefficient are calculated from the stress autocorrelation function. The ratio of the first normal stress coefficient to the viscosity is used to calculate the viscoelastic relaxation time. While the viscosity and the infinite-frequency shear modulus both increase monotonically with increasing density, the first normal stress coefficient and the viscoelastic relaxation time both decrease to a minimum at intermediate densities before increasing again. Our results for the viscosity and the first normal stress coefficient in the low-density limit both agree well with the predictions of kinetic theory.

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Section: -6mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Density dependence of the stress relaxation function of a simple fluid

2013

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“…Keshavarzi et al 13 suggest that LJ fluids exhibit viscoelastic behavior at higher densities, for example, when * Ͼ 0.7, where * = / . 3 Here is the number density and is the LJ size parameter.…”

Section: B Viscoelastic Constitutive Equationmentioning

confidence: 99%

Transient molecular dynamics simulations of viscosity for simple fluids

Thomas

Rowley

2007

The Journal of Chemical Physics

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A transient molecular dynamics (TMD) method has been developed for simulation of fluid viscosity. In this method a sinusoidal velocity profile is instantaneously overlaid onto equilibrated molecular velocities, and the subsequent decay of that velocity profile is observed. The viscosity is obtained by matching in a least-squares sense the analytical solution of the corresponding momentum transport boundary-value problem to the simulated decay of the initial velocity profile. The method was benchmarked by comparing results obtained from the TMD method for a Lennard-Jones fluid with those previously obtained using equilibrium molecular dynamics (EMD) simulations. Two different constitutive models were used in the macroscopic equations to relate the shear rate to the stress. Results using a Newtonian fluid model agree with EMD results at moderate densities but exhibit an increasingly positive error with increasing density at high densities. With the initial velocity profiles used in this study, simulated transient velocities displayed clear viscoelastic behavior at dimensionless densities above 0.7. However, the use of a linear viscoelastic model reproduces the simulated transient velocity behavior well and removes the high-density bias observed in the results obtained under the assumption of Newtonian behavior. The viscosity values obtained using the viscoelastic model are in excellent agreement with the EMD results over virtually the entire fluid domain. For simplicity, the Newtonian fluid model can be used at lower densities and the viscoelastic model at higher densities; the two models give equivalent results at intermediate densities.

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Novel methodology for the shear viscosity of confined fluids within the Maxwell viscoelastic regime

Sun

Kang

2023

Chemical Engineering Science

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High-Frequency Shear Modulus and Relaxation Time of Soft-Sphere and Lennard–Jones Fluids

Cited by 4 publications

References 23 publications

Density dependence of the stress relaxation function of a simple fluid

Density dependence of the stress relaxation function of a simple fluid

Transient molecular dynamics simulations of viscosity for simple fluids

Novel methodology for the shear viscosity of confined fluids within the Maxwell viscoelastic regime

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