Friction coefficient and viscosity of polymer brushes with and without free polymers as slip agents

Goicochea, A. Gama; López-Esparza, R.; Altamirano, M.A. Balderas; Rivera-Paz, E.; Waldo-Mendoza, Miguel A.; Pérez, Elı́as

doi:10.1016/j.molliq.2016.03.039

Cited by 19 publications

(22 citation statements)

References 47 publications

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“…[ 12 ] Computational simulation studies have reported rheological properties such as CoF and viscosity. Gama‐Goicochea et al [ 13,14 ] reported that CoF reduction and stabilization depend crucially on the migration and desorption of a fraction of erucamide molecules. When only molecules of this additive formed brushes, the predicted CoF did not correspond to the experimental behavior.…”

Section: Introductionmentioning

confidence: 99%

Relationship between the coefficient of friction of additive in the bulk and chain graft surface density through a diffusion process: Erucamide–stearyl erucamide mixtures in polypropylene films

Catarino-Centeno

Waldo-Mendoza

García‐Hernández

et al. 2021

Vinyl Additive Technology

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A relationship between chain graft density calculated by coarse‐grained simulation and the one obtained from experimental results is compared in the present work. Two slip additives for polypropylene films were studied, erucamide and stearyl erucamide. The diffusion equation (Fick's second law) was used to relate real‐time experimental results with coarse‐grained simulations and rendered slip additive surface density as a function of the coefficient of friction. The normalized surface density values obtained from the simulation showed a qualitative trend consistent with the experimentally observed results.

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Section: Introductionmentioning

confidence: 99%

Relationship between the coefficient of friction of additive in the bulk and chain graft surface density through a diffusion process: Erucamide–stearyl erucamide mixtures in polypropylene films

Catarino-Centeno

Waldo-Mendoza

García‐Hernández

et al. 2021

Vinyl Additive Technology

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“…This can be achieved by molecular simulations [29], which allow one to take into account such interactions explicitly and offer important molecular insights. For instance, Grest [30] studied the interfacial sliding of polymeric coatings using molecular dynamics (MD) simulation, and Gama Goicochea et al [31] calculated the friction coefficient of surfaces functionalized with polymer chains using dissipative particle dynamics. Sarkar et al [32] investigated the structure and hydrodynamic properties of nanocarriers under flow conditions by Brownian dynamics simulations.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic Properties of Polymers Screening the Electrokinetic Flow: Insights from a Computational Study

Sun

Jiang

et al. 2019

Polymers

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Understanding the hydrodynamic properties of polymeric coatings is crucial for the rational design of molecular transport involving polymeric surfaces and is relevant to drug delivery, sieving, molecular separations, etc. It has been found that the hydrodynamic radius of a polymer segment is an order of magnitude smaller than its physical size, but the origin of this effect does not seem to be well understood. Herein, we study the hydrodynamic properties of polymeric coatings by using molecular dynamics simulations, navigated by the continuous Navier-Stokes-Brinkman model. We confirm that the averaged hydrodynamic radius of a polymer bead is about one order of magnitude smaller than its physical radius, and, in addition, we show that it exhibits a strong dependence on the degree of polymerization. We relate this variation of the hydrodynamic radius to the structural properties and hydrodynamic shielding by surrounding polymer beads. This is done by separating the effects originating from near and far beads. For the near beads, shielding is mainly due to the two nearest beads (of the same polymer) and leads to about a 5-fold reduction in the hydrodynamic radius. Assuming the additivity of the hydrodynamic shielding by far beads, we suggest a simple model, which captures correctly the qualitative behaviour of the hydrodynamic radius with the degree of polymerization. The revealed shielding effects provide important insights relevant to the advanced modelling of hydrodynamic properties of polymeric coatings.

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“…At higher compressions, opposing brushes can interdigitate [12,13], which can increase frictional stresses by several orders of magnitude [14]. In fact, interdigitation between brushes can be switched using asymmetric brushes [15] and this can be employed to control the friction between surfaces [16].Molecular simulations have been employed extensively to obtain a microscopic picture of polymer brush friction [17][18][19][20][21][22][23][24][25][26]. With help of these simulations, friction-velocity relations have been derived [27][28][29][30][31][32].…”

mentioning

confidence: 99%

“…Molecular simulations have been employed extensively to obtain a microscopic picture of polymer brush friction [17][18][19][20][21][22][23][24][25][26]. With help of these simulations, friction-velocity relations have been derived [27][28][29][30][31][32].…”

mentioning

confidence: 99%

Polymer Brush Friction in Cylindrical Geometries

2019

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Polymer brushes are outstanding lubricants that can strongly reduce wear and friction between surfaces in sliding motion. In recent decades, many researchers have put great effort in obtaining a clear understanding of the origin of the lubricating performance of these brushes. In particular, molecular dynamics simulations have been a key technique in this scientific journey. They have given us a microscopic interpretation of the tribo-mechanical response of brushes and have led to the prediction of their shear-thinning behavior, which has been shown to agree with experimental observations. However, most studies so far have focused on parallel plate geometries, while the brush-covered surfaces might be highly curved in many applications. Here, we present molecular dynamics simulations that are set up to study the friction for brushes grafted on the exterior of cylinders that are moving inside larger cylinders that bear brushes on their interior. Our simulations show that the density distributions for brushes on the interior or exterior of these cylinders are qualitatively different from the density profiles of brushes on flat surfaces. In agreement with theoretical predictions, we find that brushes on the exterior of cylinders display a more gradual decay, while brushes on the interior of cylinders becomes denser compared to flat substrates. When motion is imposed, the density profiles for cylinder-grafted brushes adapt qualitatively differently to the shear motion than observed for the parallel plate geometry: the zone where brushes overlap moves away from its equilibrium position. Surprisingly, and despite all these differences, we observe that the effective viscosity is independent of the radius of the brush-grafted cylinders. The reason for this is that the viscosity is determined by the overlap between the brushes, which turns out to be insensitive to the exact density profiles. Our results provide a microscopic interpretation of the friction mechanism for polymer brushes in cylindrical geometries and will aid the design of effective lubricants for these systems.

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Friction coefficient and viscosity of polymer brushes with and without free polymers as slip agents

Cited by 19 publications

References 47 publications

Relationship between the coefficient of friction of additive in the bulk and chain graft surface density through a diffusion process: Erucamide–stearyl erucamide mixtures in polypropylene films

Relationship between the coefficient of friction of additive in the bulk and chain graft surface density through a diffusion process: Erucamide–stearyl erucamide mixtures in polypropylene films

Hydrodynamic Properties of Polymers Screening the Electrokinetic Flow: Insights from a Computational Study

Polymer Brush Friction in Cylindrical Geometries

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