Molecular Dynamics Studies Of The Annealing Of Carbon Peapods
| dc.contributor.author | Lee, Thong Yan | |
| dc.date.accessioned | 2020-10-26T02:20:20Z | |
| dc.date.available | 2020-10-26T02:20:20Z | |
| dc.date.issued | 2018-08 | |
| dc.description.abstract | In the past 30 years, carbon kept surprising the scientific community given the previous assumption that all carbon structures are already known. Apart from graphite, diamond and amorphous; new carbon allotropes including fullerenes, carbon nanotubes (CNT) and graphenes were discovered in year 1985, 1991 and 2004 respectively. Carbon peapod is a hybrid carbon nanostructure in which fullerenes such as C60 are encapsulated in an outer carbon nanotube. Carbon peapod can be transformed into a double-walled carbon nanotube (DWCNT) through annealing process. In essence, the fullerenes will fuse and form a smaller CNT in the outer CNT which acts as a mold/container. However there are a few research gaps in the simulations of the annealing process, e.g., potential was not applied to the outer CNT of the peapod and long range (van der Waals) interactions was ignored. In this thesis, the structures of three carbon peapods with different diameters are first constructed based on experimentally measured data. The peapods in the study are 13C60@CNT(13, 5), 13C60@CNT(14, 7) and 13C60@CNT(12, 12), where there are 13 C60 molecules in each peapod. Classical molecular dynamics (MD) simulations are performed to study the morphological transition of carbon peapods into DWCNT for the whole annealing process which lasted for 1 ns. All MD simulations are done with LAMMPS and AIREBO is chosen as the potential to simulate the inter- and intra-molecular interactions among the carbon atoms. From the simulated results it is observed that increased reactivity of the carbon peapod is associated with increasing annealing temperature. The carbon peapods transformed into DWCNT at an annealing temperature higher than 3500 K. The number of carbon rings, i.e., pentagon, hexagon, heptagon and octagon of the carbon peapods are numerically measured and sampled from the annealed structures. The rings statistics reveal an intimate relationship between the structures and the rings counts. In particular, it is found that when pentagons and heptagons are roughly the same in number, the structure is a fully annealed DWCNT. The cross-linked defects of the annealed peapods are also studied. It is found that 13C60@CNT(13, 5) has the highest cross-linked defects across all annealing temperatures due to its tight configuration. In the second part of the study, 13C60@CNT(12, 12) is annealed for 100 ns at 3500 K. The simulation period is 100 times longer than that of the previous section. While still being annealed at 15 ns, it is discovered that the structure collapses at one end of the inner CNT together with its nearby outer CNT. Surprisingly after that, the structure manages to salvage itself during the annealing process. Further investigation reveals that the self-healing mechanism occurs in two stages. The first stage of the self-healing is through vacancy reconstruction and the second stage is via the zipping mechanism. The quality of the annealed DWCNT with different annealing time are also compared. Through the execution of subroutines on the main simulations, 100 DWCNT which have been annealed for 1 ns, 2 ns, 3 ns … 99 ns and 100 ns are obtained. It is observed that the numbers of pentagons and heptagons in the structures annealed for more than 77 ns differ constantly by a margin of 12. The observation is interpreted in terms of the Euler characteristic of the carbon systems being simulated. Further investigation reveals that the topology of the annealed carbon peapod matches the topology of a pristine DWCNT. Finally, it should be emphasized that the novel simulated results presented in this thesis would not be possibly revealed if not for the lengthy simulation time. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/10605 | |
| dc.language.iso | en | en_US |
| dc.publisher | Universiti Sains Malaysia | en_US |
| dc.subject | Physics | en_US |
| dc.title | Molecular Dynamics Studies Of The Annealing Of Carbon Peapods | en_US |
| dc.type | Thesis | en_US |
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