Molecular Mobility of Crude Oils Via Electron Paramagnetic Resonance of Organic Free Radicals

This study aimed to investigate the molecular mobility of crude oils using the linewidth of the free radical electron paramagnetic resonance signal (EPR) as a molecular mobility probe. For this, aromatic and paraffinic crude oil samples were analyzed by X-band EPR spectroscopy, NMR experiments in time domain (TD-NMR), and rheometry. The variations on the half height linewidth with temperature presented a similar behavior for both samples, being related to different molecular mobility regimes. EPR results were compared to the variation of viscosity with temperature obtained by rheometry and TD-NMR. The results showed changes in the decrease trend of viscosity for the paraffinic sample at a temperature close to the range in which it is observed the transition from rigid to liquid regime in the EPR analysis. EPR technique showed more detailed information about the regime transition for the oil samples studied, which is in agreement with the results obtained by rheometry and TD-NMR.