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Journal Article 
Effect of end-groups on simultaneous oleophobicity/hydrophilicity and anti-fogging performance of nanometer-thick perfluoropolyethers (PFPEs) 
Wang, Y; Knapp, J; Legere, A; Raney, J; Li, Lei 
RSC Advances
EISSN: 2046-2069 
Simultaneously oleophobic/hydrophilic coatings are highly desirable in many important applications, e.g., anti-fogging. However, to date, such coatings have been rarely reported and the underlying mechanisms remain unclear. In the current paper, the wetting behavior of three nanometer-thick perfluoropolyether (PFPE) polymers with the same backbone but different end-groups has been studied by contact angle tests and the underlying mechanisms governing the simultaneous oleophobicity/hydrophilicity have been investigated. The experimental results indicated that the end-groups of the nanometer-thick PFPEs are critical to the simultaneous oleophobicity/hydrophilicity. PFPE polymers with different end-groups can interact with the substrate in very different ways, resulting in different packing orders and thus different inter-chain distances within the polymer nanofilms. If the inter-chain distance is appropriately small, smaller water molecules penetrate the nanofilms quickly while larger oil molecules penetrate the nanofilms much more slowly. As a result, the surface shows a higher oil contact angle (OCA) than WCA, i.e., simultaneous oleophobicity/hydrophilicity. Moreover, the effect of simultaneous oleophobicity/ hydrophilicity on the long-term anti-fogging capability has been studied by X-ray photoelectron spectroscopy (XPS) and anti-fogging tests. The results indicated that the unique simultaneous oleophobicity/hydrophilicity reduces the airborne hydrocarbon contamination and therefore improves the long-term anti-fogging performance. 
• ^Per- and Polyfluoroalkyl Substances (PFAS)
     PFPeS (2706-91-4)
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