Abstract
A series of 12 asphaltene samples extracted from heavy oils and the oxidized bitumen of different origin has been studied with high-frequency W-band (94 GHz) pulsed electron paramagnetic resonance (EPR) spectroscopy. Transverse (T2e) and longitudinal (T1e) relaxation times of the free radical (FR) and the vanadyl porphyrin (VO2+) were measured for each sample. A significant contribution of the spectral diffusion to T2e has been revealed and ascribed to the dipole–dipole interaction between the FR and VO2+. This indicates that the distance between the FR and VO2+ does not exceed a few nanometers, which means, in turn, that VO2+ can participate in construction of the asphaltene aggregates via the intermolecular interactions.
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