Effect of hydrophilic group substituent position on adhesion at the emulsified asphalt/aggregate interface

Abstract

Emulsified asphalt offers energy-saving and environmental benefits, aligning with low-carbon, high-quality development requirements. However, poor adhesion hampers the development of emulsified asphalt. The hydrophilic group substituent position significantly influences the adhesive strength at the emulsified asphalt/aggregate interface. To further elucidate this mechanism, this study employs molecular dynamics (MD) simulation techniques, focusing on the positional variations of the hydrophilic group in the sodium dodecylbenzene sulfonate molecule, particularly the SDBS2–1#, SDBS3–1#, and SDBS4–1# configurations. The objective is to enhance adhesion between these two materials. The simulation results were validated through macroscopic demulsification experiments, encompassing a comprehensive analysis of various parameters, including relative concentration distribution, diffusion coefficient, adhesion work, electron density difference, and electrostatic potential distribution. The result demonstrated a strong synergistic effect between the emulsifiers' molecular structure and the aggregates' chemical composition. The emulsifier SDBS4–1# with para-substitution enhances adhesion at the interface between the emulsified asphalt and alkaline aggregate (CaCO₃) by 50.4 %. The emulsifier SDBS2–1# with ortho-substitution enhances adhesion at the interface between the emulsified asphalt and acidic aggregate (SiO₂) by 33.3 %. Furthermore， the emulsifiers SDBS4–1# and SDBS2–1# promote the accumulation of electrons in asphalt molecules on CaCO₃ and SiO₂ surfaces, respectively. This increase in electron accumulation enhances the adhesion performance between emulsified asphalt and aggregate at their interface. Therefore, optimizing the structure of emulsifier molecules significantly increases the bonding strength between emulsified asphalt and aggregate surfaces.