Wetting Behavior of Nanoscale Thin Films of Selected Organic Compounds and Water on Model Basal Surfaces of Kaolinite

Molecular dynamics (MD) simulation and density functional theory (DFT) were applied to study the wetting behavior of nanoscale thin films of n-heptane, toluene, pyridine, and water at different thicknesses on the two model basal surfaces of kaolinite at room temperature. Despite the hydrophilicity of the basal surfaces, water exhibited the lowest affinity for them, but was statistically comparable to that of n-heptane, as quantified by the corresponding calculated monomolecular layer works of adhesion. The results are consistent with the simulations in which water molecules in monomolecular layer originally sandwiched between a monomolecular layer of aromatic compounds and the two basal surfaces departed from the surfaces, while the aromatic molecules migrated to the surfaces. However, such behavior was not observed in the cases in which water thin films contained multiple molecular layers of water. Interestingly, the corresponding calculated multimolecular layer works of adhesion of water were the highest among the compounds of interest. Analysis of the simulation data on both basal surfaces suggests that such observation is attributed to the water/water long-range charge-charge (69%, averaged over the two basal surfaces) and short-range hydrogen-bond (31%) interactions. Here, interfacial hydrogen bonds play a relatively minor role in the wetting behavior of water.