Evidence of the aggregation behaviour of asphaltenes according to the Yen-Mullins model by direct visualization of their Langmuir-Blodgett films

[Display omitted] •The asphaltene behaviour at interfaces is strongly influenced by its association.•The aggregation process at interfaces matches with the modified Yen model.•Microscopic morphologies reveal the cohesion forces of nanoaggregates and clusters. Within this work we provide an extensive experimental approach comprised by pressure-area isotherms and optical studies at interfaces (by means of Brewster angle microscopy and reflection spectroscopy) combined with electronic microscopies and mass spectrometry examination of Langmuir-Blodgett films transferred from spreading concentrations above and below the nanoaggregate-to-cluster aggregation threshold. It will be shown that the associated structures already present in the bulk solutions are preserved upon transference to a large extent and primarily determine the subsequent asphaltene film structure at the interface. The different morphologies derived from each aggregation state reveals the intermolecular cohesion forces that are of short-range character in the nanoaggregate range, while the elongated rod-like structures, mainly observed for high spreading concentrations, indicates a longer order interaction responsible for the clusters formation at high molecular packing. These features provide new evidence of a two-step aggregation process at interfaces that, for this particular asphaltene sample, matches with that predicted by the modified Yen model.