Slip boundary conditions for shear flow of polymer melts past atomically flat surfaces

Niavarani, Anoosheh; Priezjev, Nikolai V.

doi:10.1103/physreve.77.041606

Cited by 36 publications

(76 citation statements)

References 48 publications

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“…The MD results for flat crystalline walls confirm previous findings [30] that the slip length goes through a local minimum at low shear rates and then increases rapidly at higher shear rates. For periodically corrugated surfaces and wetting conditions, …”

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confidence: 81%

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Rheological study of polymer flow past rough surfaces with slip boundary conditions

Niavarani

Priezjev

2008

The Journal of Chemical Physics

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The slip phenomena in thin polymer films confined by either flat or periodically corrugated surfaces are investigated by molecular dynamics and continuum simulations. For atomically flat surfaces and weak wall-fluid interactions, the shear rate dependence of the slip length has a distinct local minimum which is followed by a rapid increase at higher shear rates. For corrugated surfaces with wavelength larger than the radius of gyration of polymer chains, the effective slip length decays monotonically with increasing corrugation amplitude. At small amplitudes, this decay is reproduced accurately by the numerical solution of the Stokes equation with constant and rate-dependent local slip length. When the corrugation wavelength is comparable to the radius of gyration, the continuum predictions overestimate the effective slip length obtained from molecular dynamics simulations. The analysis of the conformational properties indicates that polymer chains tend to stretch in the direction of shear flow above the crests of the wavy surface.

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supporting

confidence: 81%

“…The slip length was calculated by the linear extrapolation of the fluid velocity profile to zero with respect to a reference plane, which is located 0.5 σ away from the fcc lattice plane [27,30]. Figure 4 shows the rate dependence of the slip length in the same range of shear rates as in Fig.…”

Section: MD Results For Flat Wallsmentioning

confidence: 99%

Rheological study of polymer flow past rough surfaces with slip boundary conditions

Niavarani

Priezjev

2008

The Journal of Chemical Physics

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“…Even though we intend to disassociate the dynamic and structural behaviors from the thermal effect by enforcing a uniform fluid temperature, as the shear rate gets higher, the fluid temperature inside the system starts to deviate from the set temperature of T = 1.1 ε/k B . This has also been observed in other studies [24,40,41]. To examine how the fluid temperature alters as a result of the shearing, a local fluid temperature (kinetic temperature) as a function of z for each slab of the simulation cell is computed by using the kinetic energy:…”

Section: Velocity Profiles Vs Shear Ratesmentioning

confidence: 62%

Nanoscale simple-fluid behavior under steady shear

Yong

Zhang

2012

Phys. Rev. E

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In this study, we use two nonequilibrium molecular dynamics algorithms, boundary-driven shear and homogeneous shear, to explore the rheology and flow properties of a simple fluid undergoing steady simple shear. The two distinct algorithms are designed to elucidate the influences of nanoscale confinement. The results of rheological material functions, i.e., viscosity and normal pressure differences, show consistent Newtonian behaviors at low shear rates from both systems. The comparison validates that confinements of the order of 10 nm are not strong enough to deviate the simple fluid behaviors from the continuum hydrodynamics. The non-Newtonian phenomena of the simple fluid are further investigated by the homogeneous shear simulations with much higher shear rates. We observe the "string phase" at high shear rates by applying both profile-biased and profile-unbiased thermostats. Contrary to other findings where the string phase is found to be an artifact of the thermostats, we perform a thorough analysis of the fluid microstructures formed due to shear, which shows that it is possible to have a string phase and second shear thinning for dense simple fluids.

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“…He also found that the shear-rate dependence weakens as the wall stiffness decreases [17]. Niavarani and Priezjev [26] also investigated the shear-rate dependence of slip in polymer melts and observed that as shear increases, the slip length has a local minimum before rapidly increasing.…”

Section: Introductionmentioning

confidence: 94%

Effect of solid properties on slip at a fluid-solid interface

Pahlavan

Freund

2011

Phys. Rev. E

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The dependence of velocity slip at a liquid-solid interface upon the character of the solid is studied using atomistic simulation methods for Lennard-Jones model systems. The effect of the thermostatting mechanisms, often used in such simulations, is also investigated. The solid atom vibrational frequency is shown not to have a significant effect on the slip length for the range of parameters investigated; however, it is found that application of a thermostat to the fluid changes the slip length at low shear rates and results in an unphysical divergent slip behavior at high shear rates. On the other hand, removing the generated heat through the walls, which is more analogous to a laboratory condition, results in a nonlinearly decreasing slip length with shear rate that asymptotes to the no-slip limit at high shear rates. This effect is due to viscous heating, which increases the fluid temperature and pressure. A nonlinear relationship between the slip length and the shear rate collapses the shear-rate-slip-length dependence onto a single curve for a range of cases when heat is more realistically removed through the walls.

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Slip boundary conditions for shear flow of polymer melts past atomically flat surfaces

Cited by 36 publications

References 48 publications

Rheological study of polymer flow past rough surfaces with slip boundary conditions

Rheological study of polymer flow past rough surfaces with slip boundary conditions

Nanoscale simple-fluid behavior under steady shear

Effect of solid properties on slip at a fluid-solid interface

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