Experimental and molecular dynamics simulation of the effect of surfactant concentration on the wettability of bituminous coal

Currently, studies on the mechanism of coal dust wetting have largely ignored the key factor of surfactant concentration, so it is of significant scientific value to systematically investigate the effect of concentration change on the efficacy of surfactant wetting of coal dust. In this paper, with the help of macroscopic wettability experiments and molecular dynamics simulations, the wetting characteristics of SDBS surfactant on coal at different concentrations were analyzed in depth. An increase in the concentration of the SDBS surfactant solution causes the wettability of the coal to show a crest change that increases and then decreases. Coal wettability is optimized when the solution concentration reaches a specific threshold of 7 wt%. The simulation results show that SDBS surfactant mostly forms hydrogen bonds with water molecules in the form of strong hydrogen bonds, and the hydrogen bonding ability with water molecules is stronger than that of coal. There is a positive correlation between the onset distribution of water molecules within coal and the overlap region at the coal/water interface. The dynamic properties of water molecules show the order E<F<D<C<B<A. The number of highly active sites does not continuously increase with the amount of SDBS molecules adsorbed, but begins to decrease after a critical point is reached. The results of the study contribute to a theoretical framework to guide and use different types of surfactants to improve coal dust wettability at various concentration levels.