Mesoscopic probes in asphaltenes nanoaggregate structure: from perpendicular to paralleled orientation at the water-in-oil emulsions interface

It is well known that asphaltene molecules play a significant role in stabilizing emulsions of water-in-crude oil or diluted bitumen solutions. Here, the dissipative particle dynamics simulation method was employed to investigate the aggregation and orientation behaviors of asphaltene molecules at the interface of water-in-crude oil emulsions at mesoscale length. Three kinds of asphaltene model molecules with different architectural structures were employed in this work. It was found that the initially disordered asphaltenes quickly self-assembled into ordered nanoaggregates consisting of several molecules, in which the aromatic rings in asphaltenes were reoriented to form nanoaggregate structures. More importantly, the nanoaggregate structure indicates that most of the stacked polycyclic aromatic planes of island architecture asphaltenes preferred to be perpendicular to the O/W interface. However, most of the stacked polycyclic aromatic planes of archipelago architecture asphaltene tend to be parallelled to the O/W interface. Both the perpendicular and parallel nanoaggregate structures of asphaltenes form a steady protective film wrapping the water droplets which hinder the droplet-droplet coalescence. The increasing number of aliphatic chains of asphaltenes results in hindering of the pi-pi stacking interactions of polycyclic aromatic hydrocarbons, thus asphaltenes prefer to form the parallel orientation at the O/W interface. Our results provide insights into the fundamental understanding of self-assembly mechanisms of asphaltenes at O/W interface and the stabilization behaviors of water-in-oil emulsions with asphaltenes.