The reinforcing effect of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) on the interfacial characteristics and tensile behaviors of natural rubber (NR) composites were comparatively investigated using molecular dynamics simulations. A pull‐out simulation was performed to study the interfacial characteristics between CNTs, BNNTs and NR matrices. The results showed that increases of about 56.63% and 90.14% in the interfacial frictional force and interfacial shear strength were obtained for the composites by the incorporation of BNNTs than those by the incorporation of CNTs. A uniaxial tensile process was fulfilled by using the constant true strain rate method to study the mechanical properties of the NR composites reinforced by CNTs and BNNTs. The results indicated that significant increases of 22.34% and 26.59% in the Young's modulus, 4.34% and 19.28% in the yield stress, and 11.07% and 8.01% in the tensile strength were respectively achieved by the incorporation of CNTs and BNNTs as reinforcements. To deeply reveal the deformation mechanisms of the NR composites, the mean square displacement and root‐mean‐square radius of gyration of the NR chains, the fractional free volume in the NR composites, and the interfacial interaction energy were calculated and discussed accordingly.
Molecular dynamics (MD) simulations were adopted to compare the enhanced mechanical and tribological properties of nitrile rubber composites reinforced by different functionalized graphene sheets. Functional groups such as hydroxyl (OH), carboxyl (COOH), and ester (COOCH3) were adopted. The constant strain method was applied to measure the mechanical properties of graphene/nitrile rubber composites. Sandwiched molecular models were developed to investigate the tribological properties of graphene/nitrile rubber composites by applying a shear load. The MD simulation results showed that the incorporation of functionalized graphene enhanced the Young's modulus, bulk modulus, and shear modulus of the nitrile rubber matrix. In addition, the coefficient of friction and abrasion rate of the functionalized graphene/nitrile rubber composites decreased. The mechanisms for the interfacial interactions between the functionalized graphene and nitrile rubber matrix were determined by calculating the mean square displacement of rubber chains, binding energy, and the radial distribution function between functional groups and polar atoms in the rubber matrix, respectively. The results of the atomistic simulations indicated that stronger interfacial interactions and better stability and dispersion of graphene in rubber matrices can be obtained by introducing functionalized graphene. Owing to the combination of hydrogen bonding and strong van der Waals interactions, the COOH‐functionalized graphene behaves the best effect on the enhancement of mechanical and tribological properties of the nitrile rubber composites.
Molecular models and sandwiched friction models of pure PTFE and h-BN/ PTFE composite were respectively constructed to investigate the enhancement of mechanical and tribological performances of the polytetrafluoroethylene (PTFE) matrix by incorporating the hexagonal boron nitride (h-BN) nanosheets as reinforcements. The simulation results indicate that increases of 36.4% in the Young's modulus, 23.6% in the bulk modulus, and 37.3% in the shear modulus of the PTFE matrix are achieved respectively by the incorporation of h-BN nanosheets. Decreases of 3.48% and 10.27% in the Poisson's ratio and the ratio of bulk modulus to shear modulus of the PTFE matrix are also observed due to the incorporation of h-BN nanosheets, which shows that the ductility of the PTFE matrix could be somewhat decreased with the addition of h-BN nanosheets. Additionally, decreases of 69.23% and 69.06% in the coefficient of friction and friction stress of the PTFE matrix are obtained respectively with the introduction of h-BN nanosheets. To provide in-depth insight into the internal reason for these findings, the interaction energy between the PTFE matrix and h-BN nanosheets, the MSD and diffusion coefficient of PTFE chains, and the RDF of carbon and fluorine atoms in the PTFE backbone chains were evaluated and interpreted accordingly.
To comparatively investigate the mechanical, tribological, and interfacial properties of polytetrafluoroethylene (PTFE) strengthened by graphene (Gr) and hexagonal boron nitride (h‐BN) nanosheets, molecular models of PTFE nanocomposites containing a similar weight fraction of Gr and h‐BN nanosheets were established. The constant‐strain approach, the three‐layer friction structures, and the pull‐out simulations were respectively employed to calculate the mechanical, tribological, and interfacial properties of the nanocomposites. Results indicate that the Young's, shear, and bulk moduli of the nanocomposites are increased by 17.22%, 20.72%, and 4.78%, respectively, by introducing h‐BN nanosheets than those by introducing Gr nanosheets. Meanwhile, a decrease of 8.49% in the friction coefficient of the nanocomposites is obtained by incorporating h‐BN nanosheets than that by incorporating Gr nanosheets. In addition, 84.71% and 5.18 times higher in the interfacial cohesive strength and interfacial shear strength, and 91.58% and 128.7% higher in the interfacial fracture toughness of PTFE nanocomposites in the normal separation and shear separation, respectively, are achieved by incorporating h‐BN nanosheets than those by incorporating Gr nanosheets. To provide a deeper understanding of the enhancement mechanisms of h‐BN nanosheets, the interfacial interaction energies, radial distribution functions, and von Mises stress distributions of the two PTFE nanocomposites were evaluated and interpreted accordingly.
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