Cluster solvation models of carbon nanostructures: extension to fullerenes, tubes, and buds

Carbon nanobud (CNB), a hybrid material consisting of single-wall C-nanotubes (CNTs) (SWNTs) with covalently attached fullerenes, in cluster form is discussed in organic solvents. Theories are developed based on bundlet and droplet models describing size-distribution functions. Phenomena present a unified explanation in bundlet model in which free energy of CNBs involved in cluster is combined from two parts: a volume one proportional to the number of molecules n in aggregate and a surface one, to n(1/2). Bundlet model enables describing distribution function of CNB clusters by size. From purely geometrical considerations bundlet (SWNT/CNB) and droplet (fullerene) models predict dissimilar behaviors. Interaction-energy parameters of CNBs are taken from C60. A C60/SWNT in-between behavior is expected; however, properties of CNBs result closer to SWNTs. Smaller CNB clusters result less stable but greater ones are more stable than SWNT bundles. The solubility decays with temperature result smaller for SWNT/CNB than C60 in agreement with lower number of units in aggregates. Discrepancy between the experimental data of heat of solution of fullerenes and CNT/CNBs is ascribed to sharp concentration dependence of heat of solution. Diffusion coefficient decays with temperature and results greater for CNB than SWNT or C60. Clusters (C60)13 and SWNT/CNB7 are representative of droplet and bundlet models.