Oleophobicity

Oleophobicity is a property of a surface that resists wetting by oils. It is commonly described by the oil contact angle (OCA) formed by a test oil droplet on the surface; higher OCAs indicate greater oleophobicity. Unlike hydrophobicity, which pertains to water, oleophobicity focuses on oils and other nonpolar liquids. A surface can be hydrophobic yet oleophilic, so separate characterization is often needed for applications where oil repellence is important.

Achieving oleophobicity generally relies on a combination of low surface energy and appropriate surface roughness. Chemical groups such as fluorinated alkyl chains or silicone-compatible moieties lower the surface energy, reducing affinity for oils. Roughness at micro- and nano-scales can magnify oleophobic effects through Cassie-Baxter-type wetting, where oil droplets sit on air pockets rather than fully wetting the solid; re-entrant geometric features help resist wetting by low-surface-tension oils.

Measurement and standards: oil contact angles are measured using reference oils (e.g., hexadecane, mineral oil). Advancing and receding OCAs, along with shedding angle and contact angle hysteresis, quantify oleophobic performance. Some studies report oil-repellency ratings rather than angles.

Applications: oleophobic coatings are used to protect glass and plastic screens, cookware, textiles, packaging, and automotive components from grease, lubricants, and fingerprints. In electronics, oleophobic coatings reduce oily fingerprints while maintaining clarity and touch sensitivity.

Limitations: many oleophobic coatings rely on chemically bonded fluorinated materials that can raise environmental concerns. Durability under abrasion, solvents, and heat is a challenge, and real-world oils with variable composition can compromise performance. Research seeks durable, non-toxic, high-temperature oleophobic surfaces with good mechanical wear resistance.