The atomic-scale structure of petroleum asphaltenes has predominately been studied through diffraction in the solid state following precipitation from crude oil. In the 1960s X-ray diffraction measurements revealed a hierarchical structure of planar aromatic stacking, alkyl side-chain association, and clustering on length scales ranging 5-20 nm. Small-angle scattering of asphaltenes in the liquid phase has characterized the self-assembly of asphaltenes into nanoaggregates and clusters. However, no previous study has investigated the local molecular structure of asphaltenes (e.g., pi-pi stacking) in the liquid phase. In this talk we will present simultaneous measurements of the molecular and aggregation structure of asphaltenes using wide <i>Q</i>-range neutron diffraction, giving access to the SANS and diffraction regimes. The results provide valuable insight into the relationship (or lack thereof) between the extent of molecular stacking and the overall self-assembled structure. Petroleum asphaltenes were extracted from a bitumen sample, fractionated, and dispersed in deuterated 1-methylnaphthalene (1-MN). The experiments were repeated as a function of temperature up to 180°C. We discovered that there was little correlation between the molecular organization and the large-scale assembly structures. However, the asphaltenes structure on the cluster length scale did vary with temperature changes. Consequently, we conclude that the dominant properties determining the phase behavior or stability of asphaltenes is largely dependent on their peripheral chemical or structural properties, and not in the extent of pi-pi geometric stacking.

Liquid-phase neutron diffraction study of the structure of solvated asphaltenes: From molecular to the cluster length scales

255th National Meeting (2018)

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