Unraveling the molecular-micellar-colloidal structure of asphalt: From interactions to structural formation

Abstract

After nearly a century of research, the colloidal structure and homogeneous solution hypotheses of asphalt remain controversial. This study integrates wide-angle/small-angle X-ray scattering (WAXS/SAXS), quantum chemistry (QC), and molecular dynamics (MD) to confirm the existence of asphaltenes aggregates, micelles and colloids in asphalt systems, systematically revealing the formation mechanism of asphalt multilevel structures. The results show that in molecular stacking, π-π interactions dominate parallel dislocation stacking when the aromatic part is large and the branched chains are short, whereas electrostatic interactions dominate parallel dislocation or T-stacking when the aromatic part is smaller. The steric hindrance of large naphthenic rings or adjacent long chains induces angular stacking. During micelle and colloid formation, to balance intra- and inter-phase interactions, asphaltenes form parallel stacks of 6∼8 layers, which crosslink with aromatic maltenes into long, narrow rod-like micelles. These micelles further disperse and crosslink into three-dimensional (3D) network colloids. Higher asphaltene content leads to long rod-like micelles and connected 3D networks, whereas higher saturates content results in large saturates regions, short micelles and localized 3D networks. The connected network enhances deformation resistance and viscosity at low shear rates, whereas strong intermolecular interactions improve resistance to molecular motion and viscosity at intermediate to high shear rates. These findings provide multiscale insights into asphalt structure and a foundation for high-performance material design.