Experimental and molecular dynamics investigations on the effects of surfactant on the wettability of coal in acidic environment

The paper uses macroscopic experiments and microscopic molecular dynamics simulations to explore the influence of the difference of DTAB surfactant concentrations and pH conditions on the wettability of coal dust. Through contact angle measurements and Fourier transform infrared spectroscopy (FTIR) to analyze functional groups and wetting behavior in coal, a multiphase wetting and adsorption system of " water-DTAB surfactant-acidic environment-coal " was constructed by molecular dynamics simulation in conjunction with characterization experiments to study the synergistic effects of DTAB surfactant and acidic environment. The comprehensive analysis showed that the wettability of coal dust along with the increase in the concentration of DTAB surfactant showed a tendency to be enhanced and then weakened, and the wettability of coal dust along with the enhancement of the weakly acidic environment is enhanced. The DTAB surfactant at a concentration of 0.075 wt% and a weakly acidic environment with a pH of 3 exhibit optimal wetting performance on coal, which transforms the coal from its original hydrophobic state (contact angle of 99.7°) to a highly hydrophilic state (contact angle reduced to 31.8°), and the total area of the absorption peaks of the hydrophilic groups in the coal increased by 192.45 %, and the diffusion coefficient of water molecules is reduced by 0.2122 Å2/ps; CH3COOH can enhance the interaction energy between DTAB surfactants and coal molecules, as well as between coal and water molecules. It further promoted the adsorption and wetting of water molecules on coal surface, and the effect of wetting action was higher than that of single-factor action.