Hydrophobic hydration of C60 and carbon nanotubes in water

We perform molecular dynamics (MD) simulations to study the hydrophobic-hydrophilic behavior of pairs Of C-60 fullerene molecules and single wall carbon nanotubes in water. The interaction potentials involve a fully atomistic description of the fullerenes or carbon nanotubes and the water is modeled using the flexible SPC model. Both unconstrained and constrained MD simulations are carried out. We find that these systems display drying, as evidenced by expulsion of the interstitial water, when the C-60 and carbon nanotubes are separated by less than 12, and 9-10 Angstrom, respectively. From the constrained simulations, the computed mean force between two carbon nanotubes in water exhibits a maximum at a tube spacing of 5.0 Angstrom which corresponds to approximately one unstable layer of interstitial water molecules. The main contribution to the force stems from the van der Waals attraction between the carbon surfaces. The minimum in the potential of mean force has a value of - 17 kJ mol(-1) Angstrom(-1) at a tube spacing of 3.5 Angstrom. (C) 2004 Elsevier Ltd. All rights reserved.