An experimental study of the stability and dynamics of Langmuir films of fullerene derivatives and their mixtures with pentadecanoic acid

The synthesis and behavior of the Langmuir monolayers of several fullerene (C-60) derivatives is reported. True monolayers are found only for one deri vative with a 12 C-atom chain substituent. The interfacial theology of thes e monolayers has been studied by measuring the thermal capillary wave spect ra. It is found that the elasticity and the dilational viscosity increase f rom diluted monolayers to an area per molecule of approximately 150 Angstro m (2), which roughly corresponds to the equilibrium distance for the interm olecular potential of the fullerene molecules. For more compressed monolaye rs both the elasticity and viscosity decrease. These results can be qualita tively explained in terms of the model described by Evans for monolayers of C-60 (Evans, A. K. J. Phys. Chem. 1998, 102, 7016). The mixed Langmuir mon olayers of x pentadecanoic acid + (1 - x) fullerene derivative have also be en studied, for 0 less than or equal to x less than or equal to 1. True mon olayers are found up to high values of x. The monolayers present a liquid e xpanded to liquid condensed transition up to values of x corresponding to o ne fullerene molecule per six of acid. This can be interpreted in terms of the ability of the mixture to maintain the hexagonal structure characterist ic of the monolayer of pure pentadecanoic acid.