Figure 1. (IMAGE)
Caption
Macroscopic wettability differences of different α-Al2O3 crystal faces and schematic diagrams to illustrate the mechanism at the molecular level. (a) Polycrystalline alumina is highly hydrophilic, while α-Al2O3 crystal faces with (11-20), (10-10) and (0001) orientations are hydrophilic, but (1-102) crystal face is hydrophobic (inset shows the optical image of a mirror flat single crystal α-Al2O3 sample). Schematic diagrams show the composite structure of adsorbed interfacial water molecules and the exposed solid atoms. The orientations of water molecules will result in two typical status offering two lone pair electrons (b-d) or one hydrogen atom (e) at the topmost position, which, in turn, result in hydrophilic and hydrophobic, respectively.
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