Characterization of fullerenes and fullerene derivatives by small-angle neutron scattering and transmission measurements

Small-angle neutron scattering (SANS) has been shown to be an appropriate technique for the structural characterization of fullerenes in solvents with strong SANS contrast (e.g., ${\mathrm{CS}}_{\mathrm{2}}\mathrm{).}$ The dimensions of ${\mathrm{C}}_{\mathrm{60}},$ ${\mathrm{C}}_{\mathrm{70}},$ and ${\mathrm{C}}_{\mathrm{84}}$ moieties derived from neutron scattering via standard Guinier analysis are typically ∼8% higher than calculated from the atomic coordinates. However, when the SANS data are fitted to an appropriate model form factor, there is good agreement between the measured and calculated values and the results are independent of the fullerene concentration within the experimental errors. Deuterated solvents (e.g., toluene-$d_8)$ have a high scattering length density (SLD), which is close to that of ${\mathrm{C}}_{\mathrm{60}},$ ${\mathrm{C}}_{\mathrm{70}},$ and ${\mathrm{C}}_{\mathrm{84}},$ so there is virtually no SANS contrast with the solvent and these particles are practically “invisible” in such media. Conversely, the negative scattering length of hydrogen lowers the SLD, giving strong contrast with toluene-$d_8$ and SANS may therefore be used to study the size and shapes of buckyballs modified with ${\mathrm{H}}^{\mathrm{1}}$ -containing materials. These may also be studied via neutron transmission measurements and this paper describes complementary studies of cyclohexane-substituted fullerenes.