Bundlet Model for Single-Wall Carbon Nanotubes, Nanocones and Nanohorns

Bundlet Model for Single-Wall Carbon Nanotubes, Nanocones and Nanohorns

Francisco Torrens, Gloria Castellano
DOI: 10.4018/ijcce.2012010105
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This paper discusses the existence of single-wall carbon nanocones (SWNCs), especially nanohorns (SWNHs), in organic solvents in the form of clusters. A theory is developed based on a bundlet model describing their distribution function by size. Phenomena have a unified explanation in bundlet model in which free energy of an SWNC, involved in a cluster, is combined from two components: a volume one, proportional to number of molecules n in a cluster, and a surface one proportional to n1/2. Bundlet model enables describing distribution function of SWNC clusters by size. From purely geometrical differences, bundlet (SWNCs) and droplet (fullerene) models predict different behaviours. The SWNCs of various disclinations are investigated via energetic–structural analyses. Several SWNC’s terminations are studied, which are different among one another because of type of closing structure and arrangement. The packing efficiencies and interaction-energy parameters of SWNCs/SWNHs are intermediate between fullerene and single-wall carbon nanotube (SWNT) clusters; an in-between behaviour is expected. However, the properties of SWNCs, especially SWNHs, are calculated close to SWNTs. The structural asymmetry in the different SWNCs, entirely characterized by their cone angle, distinguishes the properties of some, such as P2.
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Nanoparticles (NPs) interest arises from the shape-dependent physical properties of materials at nanoscale (Faraday, 1857; Murphy et al., 2010). The occurrence of single-wall carbon nanocones (SWNCs) was used to investigate the nucleation and growth of curved carbon structures, suggesting that pentagon presence performs a fundamental role. When a pentagonal defect is introduced into a graphitic sheet (graphene, GR), via the extraction of a 60º sector from this sheet, one forms a cone sheet. Pentagon presence in an SWNC apex is analogue of that in single-wall carbon nanotube (SWNT) tip topology. The SWNT terminations attracted interest once peculiar electronic states, related to topological defects in graphite lattice, were theoretically predicted (Tamura & Tsukada, 1995). The resonant picks in the density of states were observed in SWNTs (Kim et al., 1999) and multiple-wall carbon nanotubes (MWNTs) (Carroll et al., 1997). Table 1 shows SWNT–MWNT comparison.

Table 1.
Comparison between SWNTs and MWNTs
Single layer of grapheneMultiple layer of graphene
Catalyst is required for synthesisCan be produced without catalyst
Bulk synthesis is difficult as it requires proper control over growth and atmospheric conditionBulk synthesis is easy
Purity is poorPurity is high
A chance of defect is more during functionalizationA chance of defect is less but once occurred it is difficult to improve
Less accumulation in bodyMore accumulation in body
Characterization and evaluation is easyIt has complex structure
It can be easily twisted and are more pliableIt cannot be easily twisted

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