Synergistic Wetting Mechanisms of Mixed Surfactants at Different Mixing Ratios on Anthracite: Insights from Molecular Dynamics Simulations

Anthracite dust exhibits strong hydrophobicity due to its highly aromatic structure and limited oxygen-containing functional groups, which restricts spray wetting and dust suppression efficiency. In this study, a nonionic surfactant C₁₅H₂₇FO₄ (COAD) and an anionic surfactant C₁₈H₃₆CHSO₃Na-(OCH₂CH₂)₇ (FMES) were combined to improve anthracite wettability. The effects of surfactant concentration and COAD/FMES mixing ratio on wetting performance were systematically investigated through contact-angle and surface-tension measurements. The interfacial mechanisms were further elucidated using SEM, XPS, and molecular dynamics simulations. The results showed that anthracite wettability exhibited significant dependence on both surfactant concentration and mixing ratio. When the total surfactant concentration is 0.05 wt %, it tends to stabilize, and the S3 formulation (COAD: FMES = 1:3) exhibited the lowest contact angle of 20.90°. SEM observations indicated that surfactant treatment promoted particle aggregation and interparticle adhesion, while XPS results revealed a decrease in aromatic carbon content from 91.30% to 80.32% after S3 treatment, accompanied by increased aliphatic and phenolic/ether carbon fractions. Molecular dynamics simulations demonstrated that the enhanced wettability of S3 was attributed to stronger interfacial adsorption and hydration effects. The S3 system exhibited an adsorption-layer thickness of 28.15 Å, the highest RDF peak intensity (0.273) between hydrophilic groups and water molecules, and the lowest water diffusion coefficient (0.24 × 10^-5 cm²/s), indicating enhanced interfacial water enrichment and confinement. Overall, the optimized COAD/FMES system improved anthracite wettability through synergistic surfactant adsorption, hydration interactions, and interfacial water regulation, providing theoretical guidance for the development of efficient coal-dust suppressants.