(715f) A Nanometer-Thick Ionic Liquid Coating with Simultaneously Hydrophilic/Oleophobic Behavior

Surfaces that are wettable to water more easily than to oils are highly sought-after for applications such as enhanced oil/water separation, detergentless cleaning, and long-term anti-fogging coatings. However, only a small number of these surfaces have been reported, typically consisting of fluoropolymers with multi-step modification processes. Moreover, the reported surfaces are often only mildly effective or the oleophobicity degrades with time. The tunable nature of ionic liquids (ILs) makes them an attractive coating alternative, offering endless possibilities for customization and optimization by controlling the functional groups on the organic ion substituents. For this, a functionalized ionic liquid coating (dubbed “HFILOH”) with highly fluorinated alkyl segments was developed to promote a high degree of oleophobicity on Si substrates due to the high fluorination, while maintaining a water contact angle (WCA) below 10°. The coating is only about one nanometer thick and shows robust oleophobicity, approximately 70° hexadecane contact angle (HCA), over at least 48 hours of continuous exposure. This ionic liquid outperforms previously-reported perfluoropolyether coatings of the same nature. These findings indicate that functionalized ionic liquid coatings have the potential to address the challenges of creating specially wettable surfaces. Further investigation into the mechanism and optimization of these coatings could lead to their widespread use in a numerous applications that require surfaces with controlled wettability.