Study on wetting behavior between CTAC and BS-12 with gas coal based on molecular dynamics simulation

• The effects of two different types of surfactants on the wettability of gas coal were studied. • The adsorption process of surfactant was simulated at the molecular level. • The wetting mechanism of two different surfactants was revealed. • It provides a theoretical basis for increasing the wettability of coal by adding surfactant in coal mine. To determine the influence of different types of surfactants on the wettability of gas coal from a microscopic perspective, the cationic surfactant cetyltrimethylammonium chloride (CTAC) and zwitterionic surfactant dodecyldimethylbetaine (BS-12) were selected. The effects of two different types of surfactants on the wettability of gas coal were investigated using molecular dynamics simulations. The molecular dynamics simulation results showed that the surfactant molecules could be adsorbed on the surface of gas coal molecules, and the BS-12 molecule had a stronger adsorption effect. By analyzing the relative concentration distribution curves of different systems, it could be concluded that the addition of CTAC and BS-12 increased the thickness of the adsorption layer at the water/coal interface from 21.61 Å to 27.26 Å and 32.93 Å, respectively, which is consistent with the results of the water molecular diffusion coefficient analysis. In addition, the interaction energies of CTAC and BS-12 with gas coal were −1775.18 kcal/mol and −1986.95 kcal/mol, respectively, which indicates that the adsorption process was spontaneous. Finally, contact angle experiments and X-ray photoelectron spectroscopy (XPS) analyses further verified that the wettability of BS-12 for gas coal was greater than that of CTAC.