Multi-scale simulation and experimental study on the stability mechanisms of emulsifiers at the asphalt-water interface: Electrophilic/nucleophilic effect

The disparity of the dielectric constants between asphalt and water gives rise to a non-uniform electrostatic field in the oil/water interaction environment, significantly undermining the stability of the oil-water interface. This study investigates interfacial stability mechanisms using laboratory experiments, molecular dynamics, and quantum mechanics simulations. Results show cationic emulsifiers (STAB and STAC) with HLB values of 7.85 demonstrate excellent hydrophilic-lipophilic balance, reducing interface surface tension by over 60 %. In contrast, anionic emulsifiers (KDS and SDBS) perform weaker at elevated temperatures. Cationic emulsifiers exhibit superior thermal conductivity with uniform heat distribution, reducing localized heat accumulation while enhancing system diffusivity, thereby preventing oil-water separation. The moderate HOMO-LUMO energy gap (6.540 eV) of cationic emulsifiers provides balanced reactivity and good interfacial stability, unlike KDS (7.447 eV) with lower reactivity and SDBS (4.241 eV) with intense electron transfer but increased separation risk. Anionic emulsifiers' high electrophilicity enables sulfonate groups to form strong hydrogen bonds with water molecules. In contrast, cationic emulsifiers' strong nucleophilicity allows nitrogen atoms to form stable bonds with halide ions (Br⁻, Cl⁻), enhancing oil-water interface stability.