Aggregation of model asphaltenes: effect of chain length and functional groups

The relationship between the chemical structures of natural asphaltenes and their aggregation mechanism remains poorly understood. To establish the influence of different chemical functional groups on the aggregation pathway of natural asphaltenes, a series of model triphenylene-based compounds were investigated. Synthesized with alkoxy chains of varying length and amide appendages, both with and without an acid terminating moiety, their aggregation kinetics in toluene were studied over several length scales, using a combination of dynamic light scattering (DLS) and diffusion-ordered NMR spectroscopy, complemented with GROMACS molecular dynamics (MD) simulations. The chemical structures of the polyaromatic compounds play an important role in their aggregation behavior: non-centrosymmetric model compounds were more prone to aggregation and formed large clusters. Furthermore, polar components appear to have a more significant influence than π-stacking on the driving force of aggregation, as the large clusters formed were observed to possess multiple configurations. Both amide and acid groups could generate strong attractive forces between molecules, overcoming the energy barrier imposed by the aromatic solvent and molecular core. These conclusions underline a strong structure-function relationship, of a model system examined on multiple size-scales, in a single solvent.