Direct Fluorination of Ethylene–Tetrafluoroethylene Copolymer Films in Liquid Media

Direct fluorination of polymer films using F2 gas efficiently alters their surface chemical composition and thereby modifies their physical properties. However, this process can sometimes generate environmentally undesirable low-molar-mass compounds, highlighting the need for milder approaches to expand the applicability of this technique. This study investigates direct fluorination in liquid media using an ethylene–tetrafluoroethylene (ETFE) copolymer film as a benchmark material. By optimizing the fluorination conditions, complete fluorination of the outermost layer was achieved. Fluorination induced a nonmonotonic change in static water contact angle, accompanied by a significant increase in contact angle hysteresis attributed to enhanced chemical heterogeneity on the film surface. Furthermore, neither liquid- nor gas-phase fluorination of ETFE released detectable amounts of low-molar-mass compounds. These findings advance the understanding of direct fluorination in liquid media and its impact on the molecular structure and surface properties of polymers.