Study on the wetting mechanism of SDBS with coals of different ranks based on surface free energy theory

Abstract

Surfactants to improve the wetting ability of water sprays are considered an effective method of suppressing coal dust. Sodium dodecyl benzene sulfonate (SDBS) was used to understand the wetting mechanisms of an anionic surfactant on coals of different ranks. Atomic force microscopy (AFM) experiments and molecular dynamics simulations were used to investigate the surface free energy and hydration film. The analysis showed that the hydration film thicknesses obtained by both the experiment and simulation increase and then decrease with increasing SDBS concentration, and the high-rank coal had a thicker hydration film than the low-rank coal. The electrostatic potential distribution, hydrogen bonding, Mulliken charge, and interface formation energy were analyzed to illustrate the wetting mechanism. It was confirmed that coal's wettability is mostly determined by the electrophilicity of hydrogen atoms in oxygen-containing groups, and for high-rank coal, van der Waals forces gradually become the dominant forces in the wetting of the coal by SDBS. In conclusion, surface free energy theory by MD simulation proved to be a reasonable way to reveal the wetting mechanism of surfactants on coal, and the enhancement effect of SDBS on the wettability of high-rank coal is stronger than that of low-rank coal, which contributes to the development of surfactants for practical engineering applications.