Simulating of the Cluster-nature Solvent Features of Single- Wall Carbon Nanohorns

The existence of single-wall carbon nanotubes (SWNTs) in organic solvents, in the form of clusters, is discussed [1]. A theory is developed based on a bundlet model for clusters, describing the distribution function of clusters by size [2]. The phenomena have a unified explanation in the bundlet model of clusters, in accordance with which the free energy of an SWNT, involved in a cluster, is combined from two components: a volume one, proportional to the number of molecules n in a cluster, and a surface one proportional to n 1/2. The bundlet model for clusters enables describing the distribution function of SWNT clusters by size. The droplet model is formally analogous to the one for fullerene clusters. From purely geometrical differences the models predict different behaviours. Single-wall carbon nanocones (SWNCs) of various disclinations are investigated via energetic and structural analyses [3]. Several SWNC's terminations are studied, which are different amongst each other because of the type of closing structure and the arrangement of them. The SWNC packing efficiencies, and interaction-energy parameters, are intermediate between the ones of fullerene and SWNT clusters; an in-between behaviour is expected. However, SWNC properties are calculated closer to those of fullerene and more distant from those of SWNT. The equilibrium difference between the Gibbs free energies of interaction of an SWNT with its surroundings, in the solid phase and in the cluster volume or on the cluster surface shows that, on going from C 60 (droplet) to SWNT (bundlet) the minimum is less marked (68% of C 60), which causes a lesser number of units in SWNT (n min ≈2) than in C 60 clusters (≈8). Moreover the abscissa is also shorter in SWNT (n abs ≈9) than in C 60 (≈28). In single-wall carbon nanohorns (SWNHs, droplet) the minimum is more marked (122% of C 60), but the number of units in SWNH (n min ≈8) and abscissa (n abs ≈ 28) are equal to those in C 60. Temperature dependence of SWNT solubility S shows that S decreases with temperature T, because of cluster formation. At T≈260K, the C 60 crystal presents an orientation disorder phase transition from face-centred cubic (FCC) to simple cubic (SC). The S diminution is less marked for SWNT, in agreement with lesser number of units in SWNT clusters. The T dependence of the heat of solution H in toluene, benzene and CS 2 , calculated for saturation concentration …