Glassy boundary layers vs enhanced mobility in capped polymer films

Batistakis, C Chrysostomos; Michels, Maj Thijs; Lyulin, Alexey V.

doi:10.1063/1.4811237

Cited by 23 publications

(25 citation statements)

References 30 publications

(51 reference statements)

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“…Similar behavior was observed earlier in different polymer-filler composites. 41,[89][90][91] The middle-film density is obviously decreasing upon the temperature increase due to the film expansion in constant-pressure simulations.…”

Section: A Structural Propertiesmentioning

confidence: 98%

Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

Guseva

Комаров

Lyulin

2014

The Journal of Chemical Physics

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Constant temperature–constant pressure (NpT) molecular-dynamics computer simulations have been carried out for the united-atom model of a non-crosslinked (1,4) cis-polyisoprene (PI) melt confined between two amorphous, fully coordinated silica surfaces. The Lennard-Jones 12-6 potential was implemented to describe the polymer–silica interactions. The thickness H of the produced PI–silica film has been varied in a wide range, 1 < H/Rg < 8, where Rg is the individual PI chain radius of gyration measured under the imposed confinement. After a thorough equilibration, the PI film stratified structure and polymer segmental dynamics have been studied. The chain structure in the middle of the films resembles that in a corresponding bulk, but the polymer-density profile shows a pronounced ordering of the polymer segments in the vicinity of silica surfaces; this ordering disappears toward the film middles. Tremendous slowing down of the polymer segmental dynamics has been observed in the film surface layers, with the segmental relaxation more than 150 times slower as compared to that in a PI bulk. This effect increases with decreasing the polymer-film thickness. The segmental relaxation in the PI film middles shows additional relaxation process which is absent in a PI bulk. Even though there are fast relaxation processes in the film middle, its overall relaxation is slower as compared to that in a bulk sample. The interpretation of the results in terms of polymer glassy bridges has been discussed.

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Section: A Structural Propertiesmentioning

confidence: 98%

Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

Guseva

Комаров

Lyulin

2014

The Journal of Chemical Physics

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“…The polymer material present between nanoparticles in nanocomposites has been modeled previously using capped films. 24 Therefore, the model of Nafion capped between substrates of varying hydrophilicity will be effective to provide insights into the importance of the interfacial interactions in Nafion nanocomposites.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of Substrate Hydrophilicity and Confinement Effects in Capped Nafion Films

Sengupta

Lyulin

2018

J. Phys. Chem. B

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Nafion nanocomposites for energy-related applications are being used extensively because of the attractive properties such as enhanced water retention, low unwanted crossover of electrolytes, and high proton conductivity. We present the results of the molecular dynamics modeling of Nafion films confined between two walls (substrates) of different polymer–wall interaction strengths and of different separation distances to model Nafion nanocomposites. Our goal is to provide insights into the effects of varying hydrophilicity and volume fraction of fillers/nanoparticles on the internal structure and water transport inside the Nafion membrane. The sulfur–sulfur radial distribution function first peak distance and the sulfur–oxygen (water) coordination number in the first hydration shell were negligibly affected by the wall (substrate) hydrophilicity or the film thickness. The Nafion side chains were found to bend toward the substrates with high hydrophilicity which is in qualitative agreement with existing experiments. The amount of bending was observed to reduce with increasing film thickness. However, the side-chain length did not show any noticeable variation with wall (substrate) hydrophilicity or film thickness. The water clusters became smaller and more isolated clusters emerged for highly hydrophilic substrates. In addition, the water cluster sizes showed a decreasing trend with decreasing film thickness in the case of hydrophilic substrates, which has also been observed in experiments of supported Nafion films. The in-plane water diffusion was enhanced considerably for hydrophilic substrates, and this mechanism has also been proposed previously in experiments. The in-plane water diffusion was also found to be a strong function of the substrate selectivity toward the hydrophilic phase. Our simulations can help provide more insights to experimentalists for choosing or modifying nanoparticles for Nafion nanocomposites.

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“…First, the sample preparation and the equilibration could be a problem. After all, there is broad evidence, both from various experiments (23-25) and from simulations (26)(27)(28)(29)(30)(31) that when approaching the glass transition, the dynamics becomes increasingly cooperative and, at the same time, heterogeneous. Whereas, the binding of the monomers to the substrate might enhance T g , in contrast to what was assumed in Eq.…”

Section: Introductionmentioning

confidence: 99%

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

Solar¹,

Yelash²,

Virnau³

et al. 2014

Soft Materials

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A chemically realistic model of 1,4-polybutadiene confined by graphite walls in a thin film geometry was studied by molecular dynamics simulations. The chemically realistic approach allows for a quantitative determination of a variety of experimentally accessible relaxation functions (e.g., dielectric, NMR, or neutron scattering responses). The simulations yield these experimental observables. Additionally, the simulations can be resolved as a function of distance to the solid interface on a much finer scale than experimentally possible, providing a detailed mechanistic picture of the segmental and large scale motions of polymers in the interfacial region between bulk polymer melts and solid walls. Extending the study of 1,4-polybutadiene on graphite to temperatures close to the glass transition temperature, we also address the question to what extent growing length scales associated with the glass transition influence the melt dynamics in the interphase. It was found that there is an interplay of this intrinsic slowing down with the adsorption/desorption kinetics of the chains close to the wall. It is argued that the monomer density changes near the wall can overcome the effect of rotational barriers only in a region of about 2 nm next to the wall.

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Glassy boundary layers vs enhanced mobility in capped polymer films

Cited by 23 publications

References 30 publications

Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

Molecular Dynamics Simulations of Substrate Hydrophilicity and Confinement Effects in Capped Nafion Films

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

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