Wetting Characteristics and Microscopic Synergistic Mechanism of Composite Surfactants on Coal Samples with Different Degrees of Metamorphosis

Abstract

This study investigates the effects of composite surfactants on the wettability of different coal types using a combination of macroscopic experiments, mesoscopic experiments, and microscopic molecular dynamics simulations, with coal samples of varying degrees of metamorphism as research subjects. First, contact angle and surface tension experiments were performed at the macroscopic level to determine the optimal concentration and ratio of the composite surfactants. The results showed that the composite solution formed by mixing SLES and AEO-9 in a 3:2 ratio significantly reduced both the surface tension of the solution and the contact angle of the coal samples at a mass concentration of 0.5 wt %. Second, the effects of the composite surfactants on the wetting properties of coal samples were analyzed at the mesoscopic level using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and ζ-potential measurements. The results revealed that the total content of hydrophobic groups (−CH₃, −CH₃&–CH₂, C═C) in the coal molecules was significantly reduced after treatment with the composite solution, weakening the hydrophobicity of the coal samples. Additionally, the absolute value of the surface potential of the coal samples was significantly decreased, enhancing the aggregation tendency between coal particles. This facilitated the formation of larger agglomerated coal particles, which contributed to the settling of coal dust. Simultaneously, the cracks between coal particles promoted the penetration of aqueous solutions, aiding in the wetting of the coal seam. Finally, molecular dynamics simulations were conducted to analyze the synergistic wetting mechanism of the composite surfactants at the microscopic level. The results showed that the composite surfactant molecules were effectively adsorbed onto the surface of coal molecules, facilitating the movement of water molecules to the coal surface, increasing the diffusion coefficient of water molecules, and enhancing the interaction energy within the coal/composite surfactant/water system. These findings provide valuable insights for the development of new composite surfactants with wetting effects, offering significant potential for applications in mine dust control.