RESUMO
Ab initio vdW calculations with the DFT level of theory were used to investigate hydrogen (H2) adsorption on Pt-adsorbed graphene (Pt-graphene). We have explored the most energetically favorable sites for single Pt atom adsorption on the graphene surface. The interaction of H2 with the energetically favorable Pt-graphene system was then investigated. We found that H2 physisorbs on pristine graphene with a binding energy of -0.05 eV, while the binding energy is enhanced to -1.98 eV when H2 binds Pt-adsorbed graphene. We also found that up to four H2 molecules can be adsorbed on the Pt-graphene system with a -0.74 eV/H2 binding energy. The effect of graphene layer stretching on the Pt-graphene capacity/ability for hydrogen adsorption was evaluated. Our results show that the number of H2 molecules adsorbed on the Pt-graphene surface rises to six molecules with a binding energy of approximately -0.29 eV/H2. Our first-principles results reveal that the Young's modulus was slightly decreased for Pt adsorption on the graphene layer. The first-principles calculated Young's modulus for the H2-adsorbed Pt-graphene system demonstrates that hydrogen adsorption can dramatically increase the Young's modulus of such systems. As a result, hydrogen adsorption on the Pt-graphene system might enhance the substrate strength.
RESUMO
We performed first principles calculations based on density functional theory (DFT) to investigate the effect of epoxy monomer content on the electronic and mechanical properties of single-walled carbon nanotubes (SWCNTs). Our calculation results reveal that interfacial interaction increases with increasing numbers of epoxy monomers on the surface of SWCNTs. Furthermore, density of states (DOS) results showed no orbital hybridization between the epoxy monomers and nanotubes. Mulliken charge analysis shows that the epoxy polymer carries a positive charge that is directly proportional to the number of monomers. The Young's modulus of the nanotubes was also studied as a function of monomer content. It was found that, with increasing number of monomers on the nanotubes, the Young's modulus first decreases and then approaches a constant value. The results of a SWCNT pullout simulation suggest that the interfacial shear stress of the epoxy/SWCNT complex is approximately 68 MPa. These results agreed well with experimental results, thus proving that the simulation methods used in this study are viable.
RESUMO
Application of carbon nanotubes (CNTs) instead of collagen fibers (CFs) in bone tissue is one of the proposed avenues for the enhancement of bone's mechanical properties. The mechanical behavior improvement caused by such a replacement is somehow guaranteed because of the superior mechanical properties of CNTs compared to those of CFs. But on the other side, bone is a very active and dynamic tissue, which is maintained through a lifelong coupled process of resorption and formation in order to reach an optimal configuration. Hence, the well accepted fact of the bone remodeling dependency on mechanical stimuli besides the differences in mechanical behavior of CNTs and CFs under loading can encourage one to hypothesize that such a replacement would cause an imbalance in the normal rate of bone remodeling process. Results of our finite element analysis indicate that the application of CNTs instead of CFs can cause a significant reduction in strain energy density, assumed here as the mechanical stimulus to initiate the bone remodeling process. Our results also show that this replacement may change the strain energy distribution within the bone. Based on a semi-mechanistic bone remodeling theory, it is speculated that this alteration in strain energy distribution in artificial bone can destabilize normal bone remodeling process, and therefore it is likely to cause some abnormalities in bone's mechanical and biological functions.
