Dynamic nuclear polarization in suspensions of asphaltene obtained from MC-30 liquid asphalt

Abstract

Nuclear magnetic resonance and the Overhauser effect type dynamic nuclear polarization were used to study some colloidal suspensions of asphaltene obtained from MC-30 liquid asphalt in a weak magnetic field of 1.437 mT. Intermolecular spin-spin interactions occur between diffusing nuclear spins in the solvent medium and the unpaired electron spin in the asphaltene micelles. The samples were prepared in ten pure and six mixed solvent media. The Electron Paramagnetic Resonance spectrum of the asphaltene was obtained and the saturation experiments were applied to the samples. The dipolar interaction is predominant for all suspensions. Solvent molecules can diffuse freely in and out of the asphaltene micelles making dipolar interaction. Some solvent molecules, in the same sample, can attach to the asphaltene particles for an extremely short time, forming complexes and making scalar interaction. The variation of the nuclear-electron coupling parameter with the low frequency relaxation component for each pure solvent medium and the solvent effects Of CCl4 and CS2 which do not contain proton (H-1 nucleus) were investigated using mixed solvent media. The results are compared with some other studies.