Microstructural Self-Assembly and Dynamic Mechanical Response of Aged and Unaged Asphaltenes within Confined Oil Droplet Geometries

Abstract

Understanding the microstructural self-assembly and mechanical response of unaged and oxygen-aged asphaltenes within oil droplets is essential for elucidating the stabilization mechanisms of weathered crude oil emulsions generated during oil-spill weathering and remediation. Herein, quantum chemical calculations and multiscale molecular dynamics simulations were employed to systematically evaluate the impact of oxidative molecular evolution on multibody aggregation and droplet surface properties. Results revealed that aging drove asphaltenes from a bulk-dispersed state to pronounced interfacial enrichment, narrowing the radial distribution width by 51% (from 43 Å to 21 Å) and enhancing local structural ordering (radial distribution functions peak) by 10-fold via face-to-face aromatic stacking. This interfacial orientation exposed edge heteroatoms, causing the droplet hydrophilic surface area to surge by 175% (from 16 to 44 nm2) at a 20 wt % mass fraction, while the single-molecule hydration energy intensified by 84% from −2.09 to −3.85 kcal/mol. Conversely, under dynamic nonequilibrium perturbations, polar functionalization compromised the skeletal compatibility with nonpolar light oil fractions, reducing the bulk framework-solvent coupling energy to 56% of the unaged asphaltene system. Consequently, the aged droplet deformation increment (63 nm2) reached 3.9 times that of the unaged counterpart (16 nm2). This study unravels a competitive mechanism between aging-induced 2D interfacial rigidity and 3D bulk cohesion degradation, providing a critical molecular framework for designing targeted demulsifiers to accelerate phase separation in weathered crude oils.