Water-induced interactions between carbon nanoparticles.

Molecular dynamics simulations were carried out in order to study the hydration of C60 fullerenes, carbon nanotubes, and graphene sheets in aqueous solution and the nature of water-induced interactions between these carbon nanoparticles. The hydration of these nonpolar carbon nanoparticles does not exhibit classical hydrophobic character due to the high density of surface atoms (carbon) resulting in strong water-surface dispersion interactions. Water was found to wet the nanoparticle surfaces independent of nanoparticle surface curvature, with the decrease in the extent of water-water hydrogen bonding with decreasing surface curvature being offset by stronger water-surface interactions. While all carbon nanoparticles investigated are anticipated to aggregate in water due to strong direct nanoparticle-nanoparticle interactions, the water-induced interactions between nanoparticles were found to be repulsive and, in contrast to the wetting behavior, were observed to exhibit strong dependence on surface curvature. The strength of the water-induced interaction between carbon nanoparticles was found to correlate well with the number of hydration water molecules displaced upon particle aggregation, which, relative to the amount of direct nanoparticle-nanoparticle contact engendered upon aggregation, decreases with decreasing surface curvature.