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| Author(s): |
Levi da Costa Felix
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2022-09-12 |
| Examining board members: |
Douglas Soares Galvão;
Maurice de Koning;
Renato Pavanello;
Caetano Rodrigues Miranda;
Paulo Sérgio Branício
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| Advisor: | Douglas Soares Galvão; Alexandre Fontes da Fonseca |
| Abstract | |
From diamond to graphite, carbon materials play an important role in current technology. Due to its chemical flexibility provided by different orbital (sp, sp², and sp³) hybridization, carbon can form a large variety of structures with very distinct properties. With the aid of computational tools, we studied the mechanical behavior of several carbon nanostructures, ranging from porous to two-dimensional materials. Atomistic molecular dynamics simulations were carried out to investigate mechanical properties and energy absorption of schwarzites, a porous carbon structure based on triply-periodic minimal surfaces. Compressive and tensile deformations were applied to observe deformation mechanisms and evaluate stiffness. Two structures belonging to two different families (primitive and gyroid) were studied, in which they differ mainly by their relative number of hexagonal to octagonal carbon rings that are directly related to pore size. Structures with larger pores presented better energy absorption capabilities, whereas the ones with smaller pores were found to be stiffer. Resistance to ballistic impact was also investigated. Again, large-pore structures have a better performance absorbing the kinetic energy. The porous character of schwarzites has led us to investigate the mechanical response of a newly proposed carbon allotrope called pentadiamond, a porous network of carbon pentagonal rings with mixed sp² and sp³ hybridization. By combining density functional theory with molecular dynamics, we investigated the correspondence between orbital hybridization and mechanical stiffness by comparing pentadiamond to schwarzites and diamond. Electron localization results showed that stiffer materials tend to have a more localized electronic distribution. Mechanical instabilities were also found in pentadiamond at finite temperature by molecular dynamics, where strong fluctuations in the atomic positions occur when the structure is subject to high strain levels beyond the elastic regime. The same methodology of using molecular modeling to study the mechanical properties was applied to the mechanics of some two-dimensional carbon structures. The first one consist of a suspended monolayer of amorphous carbon (MAC), that was recently synthesized. We simulated its mechanical behavior under stretching and thermal evaporation by a temperature ramp. These results are compared with those of pristine graphene. MAC was found to be more ductile while having a melting point close to that of graphene. Another problem explored in this thesis is fracture diodes in defective graphene. Following recent works that suggested microstructure manipulations by introducing an array of triangular holes in a polymer thin plate, we extended these concepts to the nanoscale by considering monolayer graphene with the same microstructure manipulation. We observed a rectification effect in the fracture propagation direction. This effect is directly related to the space between each triangular void. Another interesting feature is that such microstructure allows the fracture to propagate only in the region where the array of defects is present. Such a system can be used to design part devices where fracture, when unavoidable, can be redirected to avoid damage to critical components (AU) | |
| FAPESP's process: | 18/11352-9 - Structural, mechanical and transport properties of schwartzites |
| Grantee: | Levi da Costa Felix |
| Support Opportunities: | Scholarships in Brazil - Doctorate |