| Abstract
| - The dynamics, structure, and thermotropic behavior of a new class of lipophilic [60]fullerene (C60) derivatives,so-called lipo-fullerenes, have been studied by differential scanning calorimetry (DSC), deuterium nuclearmagnetic resonance (2H NMR), and X-ray scattering. The lipo-fullerene studied consists of six pairs ofperdeuterated C18 alkyl chains as substituents of six covalently attached methylene groups in octahedral sites.The symmetry of this highly symmetrical hexamethanofullerene is Th. We find drastic changes of the moleculararrangement of the lipo-fullerenes induced by temperature. Heating the sample from 20 to 70 °C causes it toundergo two major structural transitions. At 55 °C we observe an exothermic transition from a low-temperature,hard sphere-like packing state of the molecules, with separation distances (6.1 nm) slightly above the maximumdiameter of the molecules, to a condensed one. This latter state involves partial intercalation (interdigitation)of the alkyl chains belonging to adjacent molecules and is preceded by partial melting of the chains toaccommodate sterically for the (exothermic) interdigitation. The latter allows denser packing with an averageseparation distance of 4.8 nm. At a temperature of 64 °C, an endothermic melting transition from theinterdigitated to a viscous fluidlike state is observed, with an average separation distance of 2.8 nm. Coolingthe sample from 70 °C causes a direct transition from the fluid into the low-temperature state with nointerdigitation of the chains.
|
