FULLERENE FILMS AND FULLERENE DODECYLAMINE ADDUCT MONOLAYERS AT AIR-WATER INTERFACES STUDIED BY NEUTRON AND X-RAY REFLECTION

Neutron and X-ray reflection measurements and surface pressure isother ms of spread films of the fullerene-dodecylamine adduct C60-[NH2(CH2)1 1CH3]x all indicate that this material may form monomolecular layers o n water surfaces. The reflection data sets (neutron on both H2O and D2 O) can be accounted for by a single model structure defined in terms o f the dimensions of an average cell and its chemical composition. This model ascribes a total thickness of about 29 angstrom to the molecula r interface layer with the following internal structure. The fullerene s (with several alkyl chains attached) form a central stratum and the remainder alkyl tails are located close to both the air and the water interfaces. The alkyl moieties close to the aqueous substrate are hydr ated. The reflection experiments and the isotherms suggest that on ave rage 8 +/- 3 dodecylamine molecules are present per fullerene, consist ent within error, with elemental analysis 5 +/- 2. By contrast, neutro n reflection and surface pressure vs. area data of spread films of C60 fullerenes on aqueous surfaces indicate the formation of inhomogeneou s multilayer films with a thickness and a surface roughness exceeding the molecular size. These underivatized fullerenes thus do not form mo nomolecular films.