Static and dynamic properties of the interface between a polymer brush and a melt of identical chains

Pastorino, Claudio; Binder, Kurt; Kreer, T.; Müller, Marcus

doi:10.1063/1.2162883

Cited by 134 publications

(191 citation statements)

References 57 publications

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“…The behaviour is similar for all bending rigidities: the chains elongate in the z direction upon increasing ρ g , due to excluded volume interactions, as reported in Refs. [18,19] for brushes composed of fully flexible chains. This effect is less pronounced for the more rigid chains (k b = 8ε) and barely noticeable for the stiffest case (k b = 80ε), due to the finite extension reachable by the chains.…”

Section: A Static Propertiesmentioning

confidence: 99%

“…This means that the relation between the total force exerted on the walls and the shear rate is independent of the polymer brush, and only depends on the liquid. It was possible to extract the viscosity of the simple liquid from the relation: F x = η·A·γ, obtaining a value of η = 1.28ετ σ −3 [18,21]. This essentially shows that the liquid behaves as a simple (newtonian) liquid with a well defined viscosity for the whole range of shear rates, and that the different morphologies of brush-liquid interface or gas content inside the brush layer does not have a significative role in the diffusion of momenta in the system.…”

Section: B Flow Propertiesmentioning

confidence: 99%

“…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%

“…The system was taken out of equilibrium by moving the walls at constant velocity in opposite directions [18,22]. This induces a flow with a linear velocity profile in the liquid phase indicated in Figure 1.…”

Section: B Flow Propertiesmentioning

confidence: 99%

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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: A Static Propertiesmentioning

confidence: 99%

Section: B Flow Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: B Flow Propertiesmentioning

confidence: 99%

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

Speyer

Pastorino

2015

Soft Matter

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“…The equilibrium properties of these reference systems are interesting and have been comprehensively studied in previous works 4,15,20,21,22,23,24 . The brush layers are characterized by the number of grafted chains per unit area or grafting density ρ g .…”

Section: 614mentioning

confidence: 99%

Comparison of dissipative particle dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

et al. 2007

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In this work we compare and characterize the behavior of Langevin and Dissipative Particle Dynamics (DPD) thermostats in a broad range of non-equilibrium simulations of polymeric systems. Polymer brushes in relative sliding motion, polymeric liquids in Poiseuille and Couette flows, and brush-melt interfaces are used as model systems to analyze the efficiency and limitations of different Langevin and DPD thermostat implementations. Widely used coarse-grained bead-spring models under good and poor solvent conditions are employed to assess the effects of the thermostats. We considered equilibrium, transient, and steady state examples for testing the ability of the thermostats to maintain constant temperature and to reproduce the underlying physical phenomena in non-equilibrium situations. The common practice of switching-off the Langevin thermostat in the flow direction is also critically revisited. The efficiency of different weight functions for the DPD thermostat is quantitatively analyzed as a function of the solvent quality and the non-equilibrium situation.

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Molecular Simulation of Polymer Melts and Blends: Methods, Phase Behavior, Interfaces, and Surfaces

Virnau

Binder

Heinz

et al. 2010

Encyclopedia of Polymer Blends

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Understanding thermodynamic properties, including also the phase behavior of poly mer solutions, polymer melts, and blends, has been a long-standing challenge [1][2][3][4][5][6][7]. Initially, the theoretical description was based on the lattice model introduced by Flory and Huggins [1][2][3][4][5][6][7]. In this model, a flexible macromolecule is represented by a (self-avoiding) random walk on a (typically simple cubic) lattice, such that each bead of the polymer takes one node of the lattice, and a bond between neighboring beads of the chain molecule takes a link of the lattice. For a binary polymer blend (A,B), two types of chains occur on the lattice (and possibly also free volume or vacant sites, which we denote as ). The model (normally) does not take into account any disparity in size and shape of the (effective) monomeric units of the two partners of a polymer mixture. Between (nearest neighbor) pairs AA, AB, and BB of effective monomers, pairwise interaction energies, e AA , e AB and e BB , are assumed. Thus, this model dis regards all chemical detail (as would be embodied in the atomistic modeling [8-10], where different torsional potentials and bond-angle potentials of the two constituents can describe different chain stiffness).Despite the simplicity of this lattice model, it is still a formidable problem of statistical mechanics, and its numerically exact treatment already requires largescale Monte Carlo simulations [11][12][13]. Consequently, the standard approach has been [1-7] to treat this Flory-Huggins lattice model in mean-field approximation, which leads to the following expression for the excess free energy density of mixing [4]:1:1Here w A , w B and w V 1 w B are the volume fractions of monomers of type A, B and of vacant sites, respectively. Every lattice site has to be taken by either w A Edited by Avraam I. Isayev

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Static and dynamic properties of the interface between a polymer brush and a melt of identical chains

Cited by 134 publications

References 57 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

Comparison of dissipative particle dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

Molecular Simulation of Polymer Melts and Blends: Methods, Phase Behavior, Interfaces, and Surfaces

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