摘要：SummaryThe surface free energy of rare earth oxides (REOs) has been debated during the last decade, with some reporting REOs to be intrinsically hydrophilic and others reporting hydrophobic. Here, we investigate the wettability and surface chemistry of pristine and smooth REO surfaces, conclusively showing that hydrophobicity stems from wettability transition due to volatile organic compound adsorption. We show that, for indoor ambient atmospheres and well-controlled saturated hydrocarbon atmospheres, the apparent advancing and receding contact angles of water increase with exposure time. We examined the surfaces comprehensively with multiple surface analysis techniques to confirm hydrocarbon adsorption and correlate it to wettability transition mechanisms. We demonstrate that both physisorption and chemisorption occur on the surface, with chemisorbed hydrocarbons promoting further physisorption due to their high affinity with similar hydrocarbon molecules. This study offers a better understanding of the intrinsic wettability of REOs and provides design guidelines for REO-based durable hydrophobic coatings.Graphical abstractDisplay OmittedHighlights•REOs are intrinsically hydrophilic but become hydrophobic as they adsorb hydrocarbons•Our results demonstrate that both physisorption and chemisorption occur on the surface•The adsorption of hydrocarbons was confirmed by multiple surface chemistry analysis•Our work offers a better fundamental understanding of the intrinsic wettability of REOInorganic materials; Materials science; Materials chemistry; Materials characterization; Materials application
