scholarly journals Nanoscale friction and wear of a polymer coated with graphene

2022 ◽  
Vol 13 ◽  
pp. 63-73
Author(s):  
Robin Vacher ◽  
Astrid S de Wijn
Keyword(s):  
Molecular Dynamics ◽  
Polyvinyl Alcohol ◽  
Viscoelastic Properties ◽  
Friction And Wear ◽  
Indentation Depth ◽  
Polymer Chains ◽  
Graphene Sheets ◽  
Challenging Problem ◽  
Flat Sheet ◽  
Dynamics Simulations

Friction and wear of polymers at the nanoscale is a challenging problem due to the complex viscoelastic properties and structure. Using molecular dynamics simulations, we investigate how a graphene sheet on top of the semicrystalline polymer polyvinyl alcohol affects the friction and wear. Our setup is meant to resemble an AFM experiment with a silicon tip. We have used two different graphene sheets, namely an unstrained, flat sheet, and one that has been crumpled before being deposited on the polymer. The graphene protects the top layer of the polymer from wear and reduces the friction. The unstrained flat graphene is stiffer, and we find that it constrains the polymer chains and reduces the indentation depth.

scholarly journals Nano-scale friction and wear of polymer coated with graphene

2021 ◽  
Author(s):  
Robin S Vacher ◽  
Astrid S de Wijn
Keyword(s):  
Molecular Dynamics ◽  
Viscoelastic Properties ◽  
Friction And Wear ◽  
Indentation Depth ◽  
Polymer Chains ◽  
Graphene Sheets ◽  
Challenging Problem ◽  
Nano Scale ◽  
Flat Sheet ◽  
Dynamics Simulations

Background: Friction and wear of polymers at the nano scale is a challenging problem due to the complex viscoelastic properties and structure. Using molecular-dynamics simulations, we investigate how a graphene sheet on top of a semicrystalline polymer (PVA) affects the friction and wear.Results: Our setup is meant to resemble an AFM experiment with a silicon tip. We have used two different graphene sheets: an unstrained, flat sheet, and one that has been crumpled before being deposited on the polymer.Conclusion: The graphene protects the top layer of the polymer from wear and reduces the friction. The unstrained flat graphene is stiffer, and we find that it constrains the polymer chains and reduces the indentation depth.

Behavior of protruding lateral plane graphene sheets in liquid dodecane: molecular dynamics simulations

2016 ◽  
Vol 18 (11) ◽  
Author(s):  
Shenghui Chen ◽  
Shuangqing Sun ◽  
Chunling Li ◽  
Charles U. Pittman ◽  
Thomas E. Lacy ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Graphene Sheets ◽  
Lateral Plane ◽  
Dynamics Simulations

Vibration of Single- and Double-Layered Graphene Sheets

2011 ◽  
Vol 2 (1) ◽  
Author(s):  
Behrouz Arash ◽  
Quan Wang
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Molecular Dynamics Simulations ◽  
Nonlocal Parameter ◽  
Small Scale ◽  
Graphene Sheets ◽  
Elastic Model ◽  
Resonant Frequencies ◽  
Nonlocal Continuum Theory ◽  
Dynamics Simulations

Free vibration of single- and double-layered graphene sheets is investigated by employing nonlocal continuum theory and molecular dynamics simulations. Results show that the classical elastic model overestimated the resonant frequencies of the sheets by a percentage as high as 62%. The dependence of small-scale effects, sizes of sheets, boundary conditions, and number of layers on vibrational characteristic of single- and double-layered graphene sheets is studied. The resonant frequencies predicted by the nonlocal elastic plate theory are verified by the molecular dynamics simulations, and the nonlocal parameter is calibrated through the verification process. The simulation results reveal that the calibrated nonlocal parameter depends on boundary conditions and vibrational modes. The nonlocal plate model is found to be indispensable in vibration analysis of grapheme sheets with a length less than 8 nm on their sides.

scholarly journals Interface Characteristics of Neat Melts and Binary Mixtures of Polyethylenes from Atomistic Molecular Dynamics Simulations

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1059
Author(s):  
Sanghun Lee ◽  
Curtis W. Frank ◽  
Do Y. Yoon
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Binary Mixtures ◽  
Surface Segregation ◽  
Surface Region ◽  
Polymer Chains ◽  
Methyl Groups ◽  
Free Standing ◽  
Dynamics Simulations

Molecular dynamics simulations of free-standing thin films of neat melts of polyethylene (PE) chains up to C150H302 and their binary mixtures with n-C13H28 are performed employing a united atom model. We estimate the surface tension values of PE melts from the atomic virial tensor over a range of temperatures, which are in good agreement with experimental results. Compared with short n-alkane systems, there is an enhanced surface segregation of methyl chain ends in longer PE chains. Moreover, the methyl groups become more segregated in the surface region with decreasing temperature, leading to the conclusion that the surface-segregation of methyl chain ends mainly arises from the enthalpic origin attributed to the lower cohesive energy density of terminal methyl groups. In the mixtures of two different chain lengths, the shorter chains are more likely to be found in the surface region, and this molecular segregation in moderately asymmetric mixtures in the chain length (C13H28 + C44H90) is dominated by the enthalpic effect of methyl chain ends. Such molecular segregation is further enhanced and dominated by the entropic effect of conformational constraints in the surface for the highly asymmetric mixtures containing long polymer chains (C13H28 + C150H3020). The estimated surface tension values of the mixtures are consistent with the observed molecular segregation characteristics. Despite this molecular segregation, the normalized density of methyl chain ends of the longer chain is more strongly enhanced, as compared with the all-segment density of the longer chain itself, in the surface region of melt mixtures. In addition, the molecular segregation results in higher order parameter of the shorter-chain segments at the surface and deeper persistence of surface-induced segmental order into the film for the longer chains, as compared with those in neat melt films.

scholarly journals Dynamic Properties of Water Confined in Graphene-Based Membrane: A Classical Molecular Dynamics Simulation Study

Membranes ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 165 ◽  
Author(s):  
One-Sun Lee
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Graphene Sheets ◽  
Water Molecules ◽  
Energy Profile ◽  
Confined Water ◽  
Graphene Surface ◽  
Dynamics Simulations ◽  
Density Of Water

We performed molecular dynamics simulations of water molecules inside a hydrophobic membrane composed of stacked graphene sheets. By decreasing the density of water molecules inside the membrane, we observed that water molecules form a droplet through a hydrogen bond with each other in the hydrophobic environment that stacked graphene sheets create. We found that the water droplet translates as a whole body rather than a dissipate. The translational diffusion coefficient along the graphene surface increases as the number of water molecules in the droplet decreases, because the bigger water droplet has a stronger van der Waals interaction with the graphene surface that hampers the translational motion. We also observed a longer hydrogen bond lifetime as the density of water decreased, because the hydrophobic environment limits the libration motion of the water molecules. We also calculated the reorientational correlation time of the water molecules, and we found that the rotational motion of confined water inside the membrane is anisotropic and the reorientational correlation time of confined water is slower than that of bulk water. In addition, we employed steered molecular dynamics simulations for guiding the target molecule, and measured the free energy profile of water and ion penetration through the interstice between graphene sheets. The free energy profile of penetration revealed that the optimum interlayer distance for desalination is ~10 Å, where the minimum distance for water penetration is 7 Å. With a 7 Å interlayer distance between the graphene sheets, water molecules are stabilized inside the interlayer space because of the van der Waals interaction with the graphene sheets where sodium and chloride ions suffer from a 3–8 kcal/mol energy barrier for penetration. We believe that our simulation results would be a significant contribution for designing a new graphene-based membrane for desalination.

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