Long-Lasting Simultaneously Hydrophilic/Oleophobic Behavior of a Nanometer-Thick Ionic Liquid Coating

Surfaces more wettable to water than to oil are highly desirable for applications such as oil/water separation, detergent-free cleaning, and antifogging coatings. However, such surfaces are rare, typically relying on fluoropolymer coatings requiring multistep modification, and often lose oleophobicity with time, limiting their practical use. Ionic liquids (ILs) are promising alternatives due to their thermal and chemical stability and highly tunable structures. Here we report a functionalized ionic liquid coating with highly fluorinated alkyl segments and polar end-groups. This nanometer-thick coating achieves strong oleophobicity on silica substrates, while maintaining a water contact angle (WCA) below 10°. Importantly, the oleophobicity remains stable over extended exposure, reflecting robust wetting behavior attributed to the coating's rigid structure and limited chain relaxation. We further demonstrate that the coating enables long-term antifogging and detergent-free cleaning. These results highlight the potential of functionalized ionic liquids to address the challenge of creating surfaces with controlled, unconventional wettability.