Role of Hydroxyls in Oxide Wettability

Oxides are believed to be hydrophilic because of the strong affinity for hydroxylation at their surfaces. This letter explores the relationship between the hydroxylation of oxide surfaces and their resulting wettability. Here we demonstrate that hydroxyls increase the hydrophobicity, or reduce the wettability, of oxide surfaces by reducing the polar component of surface free energy. Using alumina as a model material, increased hydrophobicity with hydroxylation was confirmed experimentally and a correlation between the strength of the hydroxyl-driven hydrophobic response and surface treatment was demonstrated.