Molecular Dynamics Investigation of Interfacial Interactions and Wettability in Coal–SiO ₂ –Water Three-Phase Systems

Abstract Molecular dynamics simulations were conducted to examine how methylated and hydroxylated coal molecules interact with SiO 2 surfaces bearing corresponding functional groups. Coal adsorption and wetting strongly depended on both coal functional groups and substrate chemistry. Methylated coal (coalCH 3 ) formed dense, planar clusters on hydrophobic SiO 2 –CH 3 , achieving nearly complete surface coverage (contact angles: 58.5°–67.7° at the surface; 81.9o–94.4° at the tetrahedral bottom), whereas on hydrophilic SiO2–OH it formed sparse spherical or rod-like aggregates (surface: 88.4°–130.6°; bottom: 64.4°–114.4°), indicating poor wettability. Hydroxylated coal (coalOH) exhibited chain-like clusters on SiO 2 –CH 3 evolving into continuous adsorption layers, while on SiO 2 –OH it formed interconnected strip-like structures with limited spreading (surface: 62.7°–113.2°; bottom: 69.9°–71°). The energy decomposition results indicated that the interaction in coalCH 3 systems is primarily governed by van der Waals forces, whereas electrostatic contributions play a dominant role in stabilizing coalOH structures, highlighting the influence of surface functionalization on adsorption and wetting behaviors.