Thermally regulated fluorine migration balances interfacial reactivity and fluorine shielding of poly(vinylidene fluoride) fillers in epoxy coatings for enhanced CO₂ corrosion protection

To clarify how the balance between interfacial reactivity and fluorine shielding affects the barrier performance of epoxy coatings, poly(vinylidene fluoride) (PVDF) fillers with tunable surface chemistry were incorporated into an epoxy matrix. Controlled alkaline dehydrofluorination generated polar active sites and strengthened filler–matrix interactions, while subsequent thermal treatment partially restored surface fluorination through the redistribution of fluorinated chain segments. Electrochemical impedance spectroscopy showed that the 120 A coating containing 5 wt% filler exhibited the best overall corrosion protection, maintaining |Z| 0.01 Hz above 10 10 Ω·cm 2 after 185 d in 3.5 wt% NaCl followed by 55 d in 12 wt% NaCl and showing the best protection after 13 d under high-temperature/high-pressure CO 2 conditions (60 °C, 2 MPa). Molecular dynamics simulations showed that the 120 A 5 wt% model had a lower accessible free-volume fraction and markedly restricted CO 2 diffusion, whereas Cl − and H 2 O exhibited species-dependent transport behavior. The improved barrier performance is therefore attributed to enhanced interfacial integrity, reduced accessible free volume, retained fluorine shielding, and increased diffusion-path tortuosity rather than a uniform decrease in the diffusion coefficients of all penetrant species. These results demonstrate that controlled PVDF dehydrofluorination combined with thermally induced fluorine redistribution provides an effective approach to balancing interfacial compatibility and fluorine shielding for durable epoxy coatings in CO 2 -containing corrosive environments.