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Research Papers

Characterization of Interfacial Properties of Graphene-Reinforced Polymer Nanocomposites by Molecular Dynamics-Shear Deformation Model

[+] Author and Article Information
Chanwook Park

Department of Mechanical and
Aerospace Engineering,
Seoul National University,
Seoul 08826, South Korea
e-mail: hachanook@snu.ac.kr

Gun Jin Yun

Department of Mechanical and Aerospace
Engineering,
Seoul National University,
Seoul 08826, South Korea
e-mail: gunjin.yun@snu.ac.kr

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received December 23, 2017; final manuscript received April 27, 2018; published online June 18, 2018. Assoc. Editor: Harold S. Park.

J. Appl. Mech 85(9), 091007 (Jun 18, 2018) (10 pages) Paper No: JAM-17-1695; doi: 10.1115/1.4040480 History: Received December 23, 2017; Revised April 27, 2018

In this paper, we present an approach for characterizing the interfacial region using the molecular dynamics (MD) simulations and the shear deformation model (SDM). The bulk-level mechanical properties of graphene-reinforced nanocomposites strongly depend on the interfacial region between the graphene and epoxy matrix, whose thickness is about 6.8–10.0 Å. Because it is a challenge to experimentally investigate mechanical properties of this thin region, computational MD simulations have been widely employed. By pulling out graphene from the graphene/epoxy system, pull-out force and atomic displacement of the interfacial region are calculated to characterize the interfacial shear modulus. The same processes are applied to 3% grafted hydroxyl and carboxyl functionalized graphene (OH-FG and COOH-FG)/epoxy (diglycidyl ether of bisphenol F (DGEBF)/triethylenetetramine (TETA)) systems, and influences of the functionalization on the mechanical properties of the interfacial region are studied. Our key finding is that, by functionalizing graphene, the pull-out force moderately increases and the interfacial shear modulus considerably decreases. We demonstrate our results by comparing them with literature values and findings from experimental papers.

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Figures

Grahic Jump Location
Fig. 1

(a) Diglycidyl ether of bisphenol F, (b) TETA, and (c) dotted lines are the crosslink reaction sites

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Fig. 2

Three layered amorphous structure before the energy minimization and the dynamic crosslinking simulation

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Fig. 3

Graphene/epoxy system

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Fig. 4

Pull-out simulation scheme at pull-out displacement 0, 20, 40, and 70 Å

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Fig. 5

(a) Pristine graphene, (b) fragment of OH-FG before equilibration, (c) fragment of COOH-FG before equilibration, and (d) COOH-FG/epoxy system after equilibration

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Fig. 6

Representative atom sets at the upper and lower boundary of the interfacial region

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Fig. 7

Interfacial shear stress distribution estimated by the shear lag theory

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Fig. 8

Density distribution profile along the z-axis

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Fig. 9

Interfacial energy profile, I initial ascent stage, II subsequent platform stage, and III final descent stage

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Fig. 10

(a) Graphene/epoxy system at the pull-out displacement of 35 Å, (b) graphene is removed from the system, (c) average of the matrix displacement during the NPT ensemble dynamics, and (d) cell length deformation during the NPT ensemble dynamics

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Fig. 11

(a) Twenty-four atoms adjacent to graphene and (b) 24 atoms adjacent to the outer matrix

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Fig. 12

Interfacial shear modulus Gi of the graphene/epoxy system on pull-out displacement range of 15–35 Å, where the dotted line is the average value

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Fig. 13

(a) Comparison of interfacial energy and (b) pull-out force between graphene/epoxy, OH-FG/epoxy, and COOH-FG/epoxy systems

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Fig. 14

Enlarged view around the (a) graphene, (b) OH-FG, and (c) COOH-FG, where the blue dotted boxes indicate the entangled structure between the functional groups and the epoxy matrix

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Fig. 15

Interfacial shear moduli and their average of (a) OH-FG/epoxy, (b) COOH-FG/epoxy systems, and (c) their comparison

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Fig. 16

Side view at pull-out displacement 60 Å of (a) graphene/epoxy, (b) OH-FG/epoxy, and (c) COOH-FG/epoxy systems

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