Influence mechanism of dodecane on coal/water interfacial hydration structure and interactions between coal particles

To elucidate the mechanism by which dodecane affects interactions between coal particles through hydrophobic masking, coal nanoparticle models with different dodecane surface coverages (Γ) are constructed, and molecular dynamics simulations combined with umbrella sampling are performed. The interfacial assembly of dodecane, the interparticle potential of mean force (PMF), structural evolution at the coal/water interface, and interaction energies between system components are analyzed. Contact angle measurements and atomic force microscopy (AFM) force measurements are used to assess the simulated trends. The results indicate that dodecane adsorption on the coal surface is driven predominantly by van der Waals interactions. With increasing surface coverage, a transition from dispersed spreading to local aggregation and multilayer stacking is observed at Γ > 0.30 nm⁻². Meanwhile, interfacial water molecules are progressively displaced, accompanied by reductions in the structural order and compactness of the hydration layer. Combined analyses of the PMF profiles and interfacial structural evolution indicate that increasing dodecane coverage reduces the repulsive energy barriers associated with hydration layer compression and deepens the attractive potential wells between coal particles. At Γ = 0.20 and 0.30 nm⁻², the PMF wells are markedly deeper, indicating a greater tendency for coal particles to form stable, compact configurations. However, at Γ > 0.30 nm⁻², the increase in local free energy barriers is attributed primarily to compression and chain rearrangement within the thicker dodecane adsorption layer. Analysis of the interaction energies indicates that the enhanced interparticle attraction arises primarily from stronger coal-coal and coal-dodecane van der Waals interactions. The concurrent weakening of coal-water van der Waals interactions is consistent with attenuation of the interfacial hydration structure. Contact angle and AFM measurements show that both the hydrophobicity of the coal model surface and interparticle adhesion are enhanced by dodecane treatment, although the hydrophobic modification effect tends to saturate at high concentrations. These findings elucidate the coupling among interfacial structural evolution, interaction energy changes, and free energy responses during dodecane hydrophobic masking and provide a theoretical basis for interfacial regulation and optimization of reagent regimes in the flotation of difficult-to-float coal fines.