Fullerene C60: Surface Energy and Interfacial Interactions in Aqueous Systems

The underlying mechanisms of fullerene-fullerene, fullerene-water, and fullerene-soil surface interactions in aqueous systems are not well understood. To advance our understanding of these interfacial interactions, the surface properties of Buckminsterfullerene (C-60) and quartz surfaces were investigated. From application of the van Oss-Chaudhury-Good model and the Young-Dupre equation, the Lifshitz-van der Waals, acid-base, and the total surface energies of C-60 powder and quartz surfaces were calculated from contact angle measurements using the sessile drop technique. C-60 powder measurements indicate low to medium energy surfaces of 41.7 mJ/m(2) with a dominant Lifshitz-van der Waals component. In aqueous systems, hydrophobic attraction due to the high cohesion of water is the driving force for C-60 aggregation. The high free energy of hydration (Delta G(pw)(total) = -90.5 mJ/m(2)) indicates the high affinity of C-60 particles for water. Hamaker constants of 4.02 x 10(-21) J (A(pwp)) and 2.59 x 10(-21) J (A(pws)) were derived for C-60-C-60 and C-60-quartz interactions in aqueous systems. The results of this study indicate that surface energy is an important physical parameter that should be considered as a basic characterization property of fullerene nanomaterials.