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摘要
The interaction between functionalized silicon probe tips and the montmorillonite (MMT) surface was studied through density-functional theory (DFT) with the van der Waals DF (vdW-DF) to include the contribution of the vdW forces in the interaction energy of the tip/MMT interface. On the basis of the noncontact AFM (NC-AFM) technique, we modeled an explicit Si probe tip that was functionalized with sulfonic acid (SA) and ethylene glycol (EG) groups present in polymeric surfactants. Accordingly, we obtained the short-range microscopic forces to investigate the hysteresis mechanism due to the approach and retraction processes of the tips as well as tip tilt, usually leading to the topographic and dissipation image contrasts. Furthermore, it was possible assert the influence of different hydrophilicity degrees toward the oxygen sites at the silicate sheet of the MMT (001) surface, which is related to important processes of surface interaction. Our results showed both SA and EG hydrophilic functional groups are selective onto the two basal oxygen sites, which also take place in the interaction on the siloxane cavity in the MMT surface. In particular, on the basal oxygen site that interacts with the intralayer hydroxyl group, the EG tip leads to an energy dissipation due to different force pathways mainly in the repulsion region, while possible energy barriers can be overcome by approaching a larger tip tilt on the other basal oxygen site in the attraction region. This tip could then display less frequency shift on the basal oxygen sites of MMT. Therefore, our results can clarify important questions about the complexity of the interaction forces between functionalized silicon probe tips and MMT in the NC-AFM experiments. Moreover, this work provides a first-principles model to describe the hydrophilic selectivity of polymeric surfactants from the interaction between nonionic OH groups and aluminosilicate surfaces in the absence of hydrophilic ions at the interlayer region.
- 出版日期2016-6-30
