Molecular Dynamics Simulation of Fullerene C60 in Ethanol Solution

An ethanol solution containing one or two fullerene C60 molecules was studied via molecular dynamics simulation. We found that the ethanol molecules form several solvation shells around the central fullerene molecule. Radial distribution functions (RDFs) and hydrogen-bond analyses were employed to detect the structure of the ethanol molecules in the solvation shells. The ethanol molecules in the first solvation shell tend to have their nonpolar alkyl groups exposed to the C60 surface while the polar hydroxyl groups point outward to maintain a hydrogen-bond network with a clathrate-like structure. Such orientation of the ethanol molecules in the first solvation shell modulates the orientation of the ethanol molecules in the second solvation shell to have the hydroxyl groups pointing inward. The potential of mean force (PMF) between two C60 molecules in ethanol solution showed that C60 molecules tend to aggregate in the ethanol solution. There is no ethanol molecule in the intersolute area if the distance between the centers of mass of two C60 molecules is shorter than 10.2 Å. The ethanol molecules near the intersolute area tend to have their methyl groups penetrating into the intersolute region if the distance between two C60 molecules is short, although the hydroxyl groups have smaller volume. We analyzed the dynamic properties of the ethanol molecules in different solvation shells and found that the relaxation is much slower than that of water solution of C60 molecules. In addition, the relaxation of the first solvation shell is slower than that in other solvation shells. The lifetime of the hydrogen-bond in the first solvation shell is also longer than that in other solvation shells while the reorientation of the hydrogen-bonded ethanol pair contributes little to break the hydrogen-bonds.