Interfacial Mechanisms of Cationic and Anionic Emulsifiers in Asphalt Emulsions

This study investigates the interfacial characteristics and stabilization mechanisms of anionic emulsifiers (KDS and SDBS) and cationic emulsifiers (STAC and STAB) in asphalt emulsions through interfacial tension analysis, storage stability testing, and molecular dynamics (MD) simulations. The results demonstrate that cationic systems exhibit superior performance; STAC and STAB reduced interfacial tension by 63.6% and 62.6%, respectively, significantly outperforming the anionic systems (50.8% and 47.3% ). Furthermore, cationic systems maintained 5-day storage separation rates below 5%, whereas anionic systems exceeded 13%. MD simulations elucidated that cationic emulsifiers form dense interfacial monolayers through robust electrostatic interactions, characterized by an interfacial energy of −85kcal/mol and an aggregation peak of 13.26. Notably, electrostatic forces accounted for more than 65% of the total interaction energy in cationic systems. In contrast, anionic emulsifiers exhibited loose adsorption patterns due to electrostatic repulsion, resulting in a higher interfacial energy of −70kcal/mol. Hydrophilic-lipophilic balance (HLB) analysis further confirmed optimal values for cationic surfactants, whereas KDS exhibited excessive hydrophilicity. All experiments were conducted under standard conditions (60°C for interfacial tension measurement, 25°C for storage stability testing, and pH 7.0 ). These findings provide fundamental molecular-level insights for the design of high-performance emulsified asphalt.