Effect of phenyl functional groups on the adsorption behaviour of dodecyl anionic emulsifiers on oxides on the aggregate surface

ABSTRACT

Emulsified asphalt finds extensive application in pavement repair, addressing issues like road ruts and cracks. While the adsorption behaviour of emulsifiers on oxide surfaces (CaCO₃ and SiO₂) of aggregates is influenced by the presence of phenyl functional groups, the precise mechanism of this influence remains insufficiently understood. This study employs molecular dynamics models and macroscopic experiments to investigate the mechanism involving emulsifiers, sodium ions, and water at aggregate interfaces, quantifying the role of phenyl functional groups from a molecular perspective. The results reveal the following: strong electrostatic attraction between alkaline aggregates and Na⁺, leading to substantial Na⁺ adsorption. The phenyl functional groups reduce diffusion coefficient, adsorption energy, and amounts in alkaline aggregates (−34.6%, −16%, −12.5%), while increasing them in acidic aggregates (+15.9%, + 14.7%, + 27.7%). The phenyl functional groups impact hydrogen bond acceptors, TPSA, and emulsifier complexity, altering adsorption. They enhance emulsifier electrostatic potential, affecting adsorption on different surfaces. In summary, this ongoing research framework aims to fine-tune emulsifiers through the use of phenyl functional groups, enhancing adsorption strength, adsorption amount, and diffusion between emulsifiers and aggregates. This work holds great significance for optimizing emulsifier molecular structures.

HIGHLIGHTS

• Strong electrostatic attraction between Na⁺ in the emulsifier and CO₃^2- ions in the oxides (CaCO₃ and SiO₂) on the aggregate surface leads to a significant accumulation of Na⁺ on the surface of the alkaline aggregates.

• As the number of phenyl functional groups increases, the diffusion coefficient, adsorption energy, and adsorption capacity of emulsifiers in alkaline aggregate systems decrease significantly, and the opposite is true in acidic aggregate systems.

• The electrostatic potential distribution of emulsifier molecules in soap liquid is significantly affected by the hydrogen bond acceptor count, TPSA, and the complexity of the phenyl functional group.

KEYWORDS:

• Emulsifier
• adsorption behaviour
• phenyl functional group
• adsorption amount
• electrostatic potential

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the General Project of the Natural Science Foundation of Shandong Province: [grant no ZR2021ME189]; National Science Foundation of China: [grant no 52078091].