Impact of oxidative aging on asphaltene interfacial behavior and emulsion stability: Implications for water remediation

Asphaltenes are key stabilizers of oil-water emulsions in bitumen production and related wastewater systems, yet the influence of oxidative aging on their interfacial behavior remains poorly understood. Here, we systematically investigate how oxidative aging alters the physicochemical properties, aggregation behavior, and interfacial performance of asphaltenes in aqueous environments. Thermal oxidation was simulated using thin-film oven tests, followed by comprehensive experimental characterization combined with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Oxidative aging progressively introduces oxygen-containing functional groups, increasing molecular polarity and reducing solvent compatibility. As a result, oxidized asphaltenes form large aggregates whose size becomes weakly dependent on concentration, suggesting a greater tendency for persistent deposition in aquatic systems. Interfacial measurements show that oxidation enhances molecular interfacial activity while simultaneously weakening the mechanical integrity of the interfacial film. Consequently, oxidized asphaltenes form fragile interfacial structures that rupture readily and promote oil droplet coalescence in aqueous media. Theoretical simulations reveal that oxidation strengthens interfacial adsorption through enhanced hydrogen bonding with water and π-π interactions with aromatic oil components. Our results demonstrate that oxidative aging plays a dual role by increasing molecular polarity and interfacial affinity while disrupting film continuity through aggregation. This work provides fundamental insights into the structure-property relationships of aged asphaltenes and offers mechanistic guidance for improving oil-water separation and environmental water remediation.