Studies of Diffusion and Adsorption Behavior of Emulsifiers onto the Asphalt Surface Based on a Quartz Crystal Microbalance with Dissipation Monitoring and Molecular Dynamics Simulations

Emulsified asphalt is extensively utilized in a variety of applications. During the preparation process, the emulsifier diffuses from the aqueous phase and adsorbs to the surface of asphalt particles, forming an adsorption film that protects the asphalt particles and stabilizes the emulsion. In this study, a quartz crystal microbalance with dissipation monitoring and molecular dynamics simulations were employed to investigate the adsorption behavior of modified styrene-maleic anhydride emulsifiers on the asphalt surface. The effects of the emulsifier molecular structure on diffusion kinetics and film mechanical properties were examined. The study revealed that the diffusion kinetics of the emulsifier are influenced by molecular weight and hydrophobicity. In addition, emulsifier groups and their spatial arrangement significantly influence adsorption conformation, thereby affecting film rigidity. Based on the findings, a quantitative model was developed to characterize the rigidity of the adsorption film. Furthermore, an adsorption efficiency index was proposed, defined by the reduction in interaction energy between the emulsifier and asphalt before and after the emulsifier transfers from the asphalt interior to the asphalt-water interface. This index enables evaluation of the structural rationality of emulsifier molecules and provides guidance for the rational design of emulsifiers in asphalt emulsions.