Study on the influence of surfactant-nanoparticles composite system on coal's wettability

In order to clarify the influence of cationic surfactants (hexadecyl trimethyl ammonium bromide, CTAB) adding with the silica (SiO2) nanoparticles on the wettability of coal, the molecular dynamics models of water-surfactant-coal, water-nanoparticles modified surfactant-coal, and nanoparticles-surfactant in the water were established respectively. The changes law of adsorption geometry, interfacial interaction energy, relative concentration distribution and mean square displacement of water molecule in the composite system before and after modification of surfactant by nanoparticles were investigated in detail. The results have shown that the CTAB is adsorbed on coal surface, because the adsorption stability between surfactants and coal is higher than that between water and coal under the electrostatic interaction. CTAB reverses the wettability of coal surface by weakening the interaction between water and coal, which promotes the transformation of the coal surface from hydrophilic to hydrophobic. Increasing concentration of surfactant can enhance the hydrophobicity of coal surface. After cationic surfactant is grafted onto nanoparticles, the particle surface changes from strong hydrophilic to hydrophobic and then to hydrophilic again with the increase of surfactant concentration. Because of the strong intermolecular force, the water molecules are bound and cannot migrate to coal surface, leading to the diffusion coefficient of water decreasing from 6.357×10-9 m2/s to 4.648×10-9 m2/s. The surfactant modified by nanoparticles improves the hydrophobicity of coal more significantly under the same concentration of the surfactant. © 2022, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.