Experimental and molecular simulation study on the influence of chain length and anion structure of ionic liquids on the wettability of highly hydrophobic bituminous coal

The wettability of bituminous coal is critical for the coal dust suppression and can be apparently modulated by ionic liquids. However, the modulation mechanism still remains elusive. Here, a combination of macroscopic experiments, mesoscopic characterization, and microscopic simulations (quantum mechanics and molecular dynamics) are leveraged to parse the effect on the wettability of coal dust surfaces of three novel ionic liquids ([C12MIm]Br, 12 MIm]Br, [BMIm]Br, [BMIm]Cl) featuring the varying chain lengths and anions in the coal-water system. The results show that the selected ionic liquids exert a distinct bridging function from traditional surfactants which invoke the hydrogen bonding interaction. This ionic liquids-mediated bridging mechanism heavily depends on their chain length structure, which can firstly penetrate deeply the internal pores of coal dusts and then adsorb on the coal surfaces to rapidly strike a dynamic equilibrium. Ionic liquids interacting with coal dust can primarily reduce the energy difference between polar and nonpolar interactions within coal dust, thereby enhancing the electrostatic interactions between coal dust and water molecules and effectively improving coal dust wetting properties. These findings provide a theoretical basis for the rational design of high-performance ionic liquids for coal mine dust control.