The viscoelastic-surfactant micelle structures on the water-wetting behaviors of bituminous coal with nuclear magnetic resonance and molecular dynamic simulation

This work presents an investigation of the influence of the formed micelle structure by viscoelastic surfactants (VES) on coal wettability with experimental and molecular simulation methods. A series of lab tests have been carried out to quantify the dynamic water migration and wetting behaviors of cetyltrimethylammonium chloride (CTAC) solutions with different concentrations in coal at 303.15 K. The results indicate that CTAC solutions can significantly promote water flow in smaller coal pores at a critical solution concentration of 1% wt. of CTAC. The contact angle decreases by about 80% with the increased solution concentration. However, the content of the hydrophilic functional groups of coal only has less than a 1% decrease. Molecular modeling of the water, CTAC, and coal system shows that the CTAC molecules form a micelle structure that would adsorb on the coal surface within the water. Because the generated micelle structure could increase the interaction energy between water and coal. It causes the reduction of the diffusion coefficient of water molecules. It is conducive to the stable adsorption of water molecules on the coal surface. Nevertheless, large CTAC clusters having a strong attraction to water molecules are counterproductive to the diffusion of water molecules on coal surfaces.