Repulsive solvent-induced interaction between ${\mathrm{C}}_{60}$ fullerenes in water

The role of water-fullerene interactions in the behavior of ${\mathrm{C}}_{60}$ in aqueous solution was investigated utilizing realistic Lennard-Jones (LJ) and repulsive Weeks-Chandler-Anderson (WCA) potentials. Strong water-fullerene dispersion interactions in the LJ potential dramatically influence the hydration of the fullerene promoting the formation of a high-density hydration shell of water. In contrast to the WCA potential, the water liquid phase between fullerenes remains stable with decreasing fullerene separation, resulting in a repulsive solvent-induced contribution to the fullerene potential of mean force.

Figure 1

The relative density of interfacial water as a function of interface thickness (relative to the surface of a ${\mathrm{C}}_{60}$ fullerene) for various water-${\mathrm{C}}_{60}$ potentials. The arrow shows the first hydration shell. The inset shows the water-${\mathrm{C}}_{60}$ pair distribution function as a function of the distance between the fullerene center of mass and the water oxygen atom.

Figure 2

The solvent-induced contribution to the potential of mean force between two ${\mathrm{C}}_{60}$ fullerenes in water for the LJ and WCA water-${\mathrm{C}}_{60}$ potentials. The inset shows the total potential of mean force between ${\mathrm{C}}_{60}$ fullerenes in water and vacuum.

Figure 3

Comparison of the structure of interfacial water for the LJ and WCA water-${\mathrm{C}}_{60}$ potentials. (a) Number of water-water hydrogen bonds per oxygen as a function of distance from the fullerene surface for various potentials; the arrow indicates the first hydration shell. (b) Relative density of water in a cylinder of radius $3.5\mathrm{\AA }$ between two ${\mathrm{C}}_{60}$ fullerenes as a function of separation between fullerene surfaces. (c) Distribution of densities in the cylinder between two ${\mathrm{C}}_{60}$ fullerenes for separations 4.0 (filled symbols) and $10.0\mathrm{\AA }$ (open symbols) for the LJ and WCA water-${\mathrm{C}}_{60}$ interactions as well as the density distribution in the equivalent volume in bulk water.