Experimental and molecular dynamics study on the influence of surfactants on the wettability of different rank coal

This study sought to enhance the wettability of coal surfaces to minimize coal mine dust generation and improve underground working conditions. To this end, we evaluated the effect of different surfactants on different coal ranks. Through molecular dynamics simulations, we constructed different coal-surfactant-water molecular systems and elucidated the microscopic migration pattern of water molecules on coal surfaces. Our findings thus provided insights into the wetting mechanisms of coal of varying ranks from multiple perspectives. Our findings indicated that the wettability of coal decreases with higher coal metamorphism. However, adding surfactants to water significantly improves the wetting effect of liquids on coal. Notably, a 1.0 wt% sodium dodecyl sulfate (SDS) solution exhibited the smallest indirect contact angles with long flame coal and gas coal samples, measuring 25.1 degrees and 25.8 degrees, respectively. Conversely, a coconut diethanolamide (CDEA) solution at a 1.0 wt% concentration demonstrated superior wetting effects on anthracite coal samples, with a contact angle of 25.7 degrees. Upon surfactant addition, the diffusion coefficient of water molecules notably increased, with maximum values reaching 2.32 & Aring;2/ps, 2.56 & Aring;2/ps, and 2.15 & Aring;2/ps, respectively. Moreover, both the total potential energy of the coal molecular layer and the surface electrostatic potential exhibited an increasing trend. This enhancement strengthens the adsorption capacity of coal molecular surfaces for water molecules, thereby promoting coal wettability. Collectively, our findings provide new insights for optimizing surfactant use and efficiently mitigating dust in coal mines.