Experiments and molecular dynamics simulations on the adsorption of naphthalenesulfonic formaldehyde condensates at the coal-water interface

Naphthalenesulfonic formaldehyde condensates (NSFCs) are widely used as dispersants in coal-water slurries (CWSs). CWS preparation tests revealed that NSFCs were favourable for viscosity reduction. The results of adsorption and contact angle measurements illustrated that a single-layer adsorption process occurred and that NSFCs decreased the hydrophobicity of Jinjie coal (JC). A molecular structural model of JC was constructed based on elemental analysis, solid state C-13 nuclear magnetic resonance (C-13 NMR) and X-ray photoelectron spectroscopy (XPS) results using a molecular dynamics (MD) simulation in Materials Studio (MS). The accuracy of the molecular structural model and the bulk model were validated by comparison with the C-13 NMR and density results, respectively. The model of the coal-water interface was investigated to analyse the dispersion mechanism of NSFCs in CWS. The results suggested that NSFCs had a unique performance with regard to viscosity reduction, which was attributed to the increased ratio of free water confirmed by the density profiles. The presence of NSFCs that made higher mobility of water caused the state of water to change from bound to free and improved the hydrophobicity of the JC surface in terms of the diffusion constant.