Linking Mineral Surface Chemistry to the Interfacial Adsorption of Ionic Emulsifiers

Adsorption of ionic emulsifiers on mineral surfaces governs interfacial processes involved in emulsified asphalt systems, yet the fundamental relationship between mineral surface chemistry and adsorption remains elusive. Herein, five representative mineral components (CaCO3, Al2O3, Fe2O3, SiO2, and MgO) were employed as model surfaces to elucidate how mineral surface chemistry regulates the adsorption of anionic sodium dodecyl benzenesulfonate (SDBS) and octadecyl trimethylammonium chloride (OTAC) using conductivity measurements, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. The results reveal that mineral surface chemistry, rather than specific surface area alone, plays a dominant role in determining adsorption affinity and selectivity. SDBS exhibited relatively high adsorption on Al2O3 and SiO2, whereas OTAC preferentially adsorbed on CaCO3 and Al2O3, demonstrating distinct mineral-dependent adsorption selectivity. Molecular simulations showed that stronger adsorption was generally accompanied by greater interfacial enrichment, stronger interaction energies, and lower molecular mobility, while the hydration environment of the ionic headgroups varied with mineral type. The different adsorption behaviors of SDBS and OTAC further reflect differences in the interactions between their ionic headgroups and mineral surfaces, as well as differences in molecular structure, with OTAC additionally exhibiting stronger intermolecular association associated with its longer hydrophobic chain. DFT calculations revealed pronounced heterogeneity in the local electrostatic environments of mineral surfaces and electrostatic complementarity between emulsifier headgroups and surface sites. These findings demonstrate that ionic emulsifier adsorption is governed by the combined effects of mineral surface chemistry, headgroup-surface interactions, interfacial hydration, and intermolecular association. This work provides fundamental insights into surfactant adsorption on mineral surfaces and offers a physicochemical basis for understanding and regulating interactions between aggregates and emulsifiers in emulsified asphalt.