Normal and Shear Forces Between Polymer Brushes

Grest, Gary S.

doi:10.1007/3-540-69711-x_4

Cited by 179 publications

(220 citation statements)

References 105 publications

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“…However, the vast majority of work was devoted to fully flexible polymer chains. Computer simulation of coarse-grained systems studied friction of bearing brushes [14][15][16][17] and the flow of simple liquids or polymer melts confined in brush-coated polymer channels as function of grafting density, interface properties and flow intensity [18][19][20][21][22]. Milchev and Binder studied the structure of brushes formed by semiflexible chains by Monte Carlo and molecular dynamics simulations [23].…”

Section: Introductionmentioning

confidence: 99%

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Speyer

Pastorino

2015

Soft Matter

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We performed molecular dynamics simulations to study equilibrium and flow properties of a liquid in a nano-channel with confining surfaces coated with a layer of grafted semiflexible polymers. The coverage spans a wide range of grafting densities from essentially isolated chains to dense brushes. The end-grafted polymers were described by a bead spring model with an harmonic potential to include the bond stiffness of the chains. We varied the rigidity of the chains, from fully flexible polymers to rigid rods, in which the configurational entropy of the chains is negligible. The brushliquid interaction was tuned to obtain a super-hydrophobic channel, in which the liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter state. Equilibrium properties such us brush height and bending energy were measured, varying the grafting density and the stiffness of the polymers. We studied also the characteristics of the brush-liquid interface and the morphology of the polymers chains supporting the liquid for different bending rigidities. Non-equilibrium simulations were performed, moving the walls of the channel in opposite directions at constant speed, obtaining a Couette velocity profile in the bulk liquid. The molecular degrees of freedom of the polymers were studied as a function of the Weissenberg number. Also, the violation of the no-slip boundary condition and the slip properties were analyzed as a function of the shear rate, grafting density and bending stiffness. At high grafting densities, a finite slip length independent of the shear rate or bending constant was found, while at low grafting densities a very interesting non-monotonic behaviour on the bending constant is observed.

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Section: Introductionmentioning

confidence: 99%

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Speyer

Pastorino

2015

Soft Matter

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“…In this paper, we will focus on the effect that solvent flow past a polymer brush has on the properties of this brush. 11 As yet, no fully satisfactory answer to the question what happens to a polymer brush under shear seems to have emerged from the literature.…”

Section: Introductionmentioning

confidence: 99%

Simulating Tethered Polymer Layers in Shear Flow with the Dissipative Particle Dynamics Technique

Wijmans

Smit

2002

Macromolecules

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The dissipative particle dynamics (DPD) method is used to simulate shear flow between two flat plates. To test this technique, simulations were conducted of both constant and oscillatory shear of a simple fluid. The results of these simulations agree well with theoretical predictions. We subsequently applied our model to study the effect of shear flow on end-tethered polymer layers ("brushes"). When exposed to a constant shear flow, chains in a polymer brush are stretched in the direction of the flow, and the overall layer thickness decreases. This result is similar to what was found in previous simulation studies. However, in the present simulations solvent particles are taken into account explicitly. At low frequencies, the response of a brush to oscillatory shear is qualitatively similar to its response to constant shear. As the flow velocity changes during an oscillation cycle, the polymer chains are able to relax their configurations with respect to the shear rate. At higher frequencies the interpretation of the brush behavior becomes more difficult due to conflicting time scales of the polymer and solvent dynamics in the present DPD model.

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“…The behavior of functionalized nanoparticles depends strongly on the attached groups. The behavior of bare, nonfunctionalized nanoparticles has been studied via experiments, theory, and simulation, as have the interactions of polymer-grafted surfaces [1,2,3,4]. The hydrodynamic and nanoparticle-nanoparticle interactions involving small functionalized nanoparticles, however, are harder to characterize.…”

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confidence: 99%

Forces between functionalized silica nanoparticles in solution

et al. 2009

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To prevent the flocculation and phase separation of nanoparticles in solution, nanoparticles are often functionalized with short chain surfactants. Here we present fully-atomistic molecular dynamics simulations which characterize how these functional coatings affect the interactions between nanoparticles and with the surrounding solvent. For 5 nm diameter silica nanoparticles coated with poly(ethylene oxide) (PEO) oligomers in water, we determined the hydrodynamic drag on two approaching nanoparticles moving through solvent and on a single nanoparticle as it approaches a planar surface. In most circumstances, macroscale fluid theory accurately predicts the drag on these nano-scale particles. Good agreement is seen with Brenner's analytical solutions for wall separations larger than the soft nanoparticle radius. For two approaching coated nanoparticles, the solvent-mediated (velocity-independent) and lubrication (velocity-dependent) forces are purely repulsive and do not exhibit force oscillations that are typical of uncoated rigid spheres.There is increasing interest in using nanoparticles in commercial and industrial applications. However, effective processing of nanoparticles requires that they do not aggregate and often involves solvation in a fluid. Functionalizing the nanoparticles accomplishes both goals. The behavior of functionalized nanoparticles depends strongly on the attached groups. The behavior of bare, nonfunctionalized nanoparticles has been studied via experiments, theory, and simulation, as have the interactions of polymer-grafted surfaces [1,2,3,4]. The hydrodynamic and nanoparticle-nanoparticle interactions involving small functionalized nanoparticles, however, are harder to characterize. Experimentally, it is difficult to manipulate and measure forces on individual nanoparticles smaller than ∼ 100 nm. Theoretical treatments are challenging because the coatings are relatively short, while the particles themselves are outside the large radius of curvature limit. Numerical simulations of discrete solvent effects on nanoparticles have been impractical until now because of the large systems required to avoid significant finite-size effects due to the long-range hydrodynamic interactions. For single-particle diffusion, these corrections have been shown [5,6] to scale as R/L where R is the particle radius and L is the simulation cell length.Recent studies have computed the potential of mean force for bare silica nanoparticles in an aqueous medium, with and without electrolytes present [7]. Forces between bare colloidal nanoparticles have also been studied in LennardJones fluids and in n-decane [8]. Hydrodynamic drag influenced by approach to a plane surface has been studied theoretically [9] and compared to simulations for rigid spheres [10,11]. Alignment effects for amorphous nanoparticles have also been studied [12]. Kim et al.[13] used molecular dynamics (MD) simulations to study the relaxation of a fullerene molecule coated with poly(ethylene oxide) (PEO). Other simulations have either relied u...

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Normal and Shear Forces Between Polymer Brushes

Cited by 179 publications

References 105 publications

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Simulating Tethered Polymer Layers in Shear Flow with the Dissipative Particle Dynamics Technique

Forces between functionalized silica nanoparticles in solution

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