Hydrophobicity of Rare Earth Oxides: Contrasting Perspectives and Emerging Insights.

The wettability of rare earth oxides (REOs) including the lanthanide series, scandium, and yttrium has become a subject of increasing interest and debate. While many studies report hydrophobic behavior with high water contact angles, emerging evidence indicates that pristine REO surfaces are intrinsically hydrophilic, and that hydrophobicity arises primarily from extrinsic surface contamination by volatile organic compounds. This perspective examines the contrasting viewpoints on REO surface wettability, integrating insights from surface structure, electronic configuration, and environmental interactions. We evaluate how factors such as crystal orientation, defect density, and chemical bonding influence water-surface interactions and contribute to the dynamic nature of REO hydrophobicity. Particular attention is given to recent findings that link hydrocarbon adsorption to changes in surface energy, and to how synthesis and surface modification techniques can tailor wettability. This evolving understanding has broad implications for applications in catalysis, biomedicine, coatings, and energy. We propose that future research should focus on isolating intrinsic surface properties from environmental effects to achieve precise control over REO wettability.