Effect of surfactant liquid temperature on wettability of bituminous coal: An experimental and molecular dynamics simulation study

Current studies on coal dust wettability seem to lack consideration of the effect of surfactant temperature. Therefore, the dust reduction mechanism of the thermal spray injected from the roadheader is still unclear. In this research, the effects of Fatty alcohol ether sulfate (AES) solutions at four temperatures (298, 308, 318, and 328 K) on the wettability of bituminous coal were investigated by experimental combined with molecular dynamics simulations. Through contact angle and settling experiments, our findings demonstrated that raising the temperature enhanced the wettability of AES surfactant solution on bituminous coal. Furthermore, the infrared spectrum (FTIR) experiment revealed that raising the AES solution temperature improves the hydrophilicity of bituminous coal. On the microscopic scale, the Water-AES-Coal system was established based on COMPASS II force field, and the molecular dynamics simulations were performed to study the water and AES molecules adsorption on the coal at different temperatures. The simulation results showed that as the temperature increased, the interaction and the thickness of adsorption layer between AES and coal molecules increased with temperature. Additionally, the water molecules' diffusion coefficient increases with the increase of simulated temperature, reaching 5.6 x 10-9 m2/s at 328 K, thus accelerating the movement of water molecules toward coal molecules which enhanced the surfactant wetting performance. Based on the experiments and simulation results, the wettability of the four temperature AES surfactants on bituminous coal was 328 K > 318 K > 308 K > 298 K. The results of the study provide a theoretical basis for guiding the use of surfactants to increase coal dust wetting under different water temperature conditions.