Direct Fluorination of Ethylene–Tetrafluoroethylene Copolymer Films in Liquid Media

Direct fluorination of polymer films using F 2 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.