Synergistic wettability enhancement and methane desorption regulation of highly hydrophobic anthracite by ammonium dodecyl sulfate-rhamnolipid composite surfactant

To enhance the wettability of highly hydrophobic anthracite and enable synergistic control of coal dust and methane hazards, this study develops binary composite system of ammonium dodecyl sulfate (ALSA) and rhamnolipid, and investigates its effects on coal wettability and methane desorption. Macroscopic characterization combined with molecular dynamics (MD) simulations reveal the interfacial mechanism. ALSA and rhamnolipid perform best; the 2:3 mass ratio yields the strongest synergy: surface tension drops to 21.8 mN/m and contact angle to 21.03°, achieving efficient coal hydrophilization. Zeta potential results show the 2:3 system achieves the highest slipping-plane surface charge density, enhancing interfacial hydration and wettability. MD simulations show the 2:3 system forms a well-connected interfacial hydrogen bond network, with the highest water diffusion coefficient and thickest water-coal overlap — key microscopic drivers of water infiltration. Methane desorption tests show the 2:3 system cuts Langmuir maximum adsorption capacity by 36.99 %; at 2.5 MPa, cumulative desorption is 38.7 % higher than raw coal. Capillary force analysis shows pore wetting shifts from a resistance-dominated state to spontaneous imbibition. Through synergistic adsorption, hydrogen bonding and diffusion optimization, the system simultaneously improves wettability and desorption, providing a theoretical basis for synergistic control of coal dust and methane hazards in underground mines.