Enhanced structural, thermal and electrochemical properties of epoxy coatings with UF/PFOTES- ZIF-8 self-healing microcapsules

This study investigates the structural, morphological, thermal, electrochemical, and self-healing properties of epoxy coatings containing microcapsules synthesized from urea-formaldehyde (UF), perfluorooctyltriethoxysilane (PFOTES), and ZIF-8 hybride. Fourier-transform infrared (FT-IR) spectroscopy confirms the successful formation of a hybrid polymeric-silane shell, revealing characteristic functional groups. Transmission electron microscopy (TEM) demonstrates a core-shell morphology of the microcapsules, indicating effective encapsulation. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) show the influence of microcapsules on the thermal properties, with reduced glass transition temperature (Tg) and enhanced thermal stability of the coating. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) provide visual and elemental evidence of self-healing, with localized release of healing agents upon damage and diffusion over time. Electrochemical impedance spectroscopy (EIS) reveals that the microcapsule-containing coatings maintain high charge transfer resistance (Rct) and coating resistance (Rcoat) in 3.5 % NaCl, demonstrating prolonged corrosion resistance and self-healing capabilities. The study highlights the potential of UF/PFOTES microcapsules to enhance coating durability, flexibility, and resistance to environmental stress. Quantitatively, Tg decreased from 113.8 °C to 90.0 °C, and thermal degradation onset was delayed by ∼28 °C with a peak at 450 °C. Rct increased sixfold from 3.23 × 10 4 Ω (bare) to 2.19 × 10 6 Ω (MUF-1 week), maintaining 1.67 × 10 6 Ω after 2 weeks. Corrosion current density dropped from 1.64 × 10 −4 A·cm −2 to 2.71 × 10 −6 A·cm −2 , with polarization resistance reaching 5.24 × 10 8 Ω·cm 2 . Adhesion recovered from 3.8 to 6.4 MPa within 7 days, confirming durable autonomous repair in aggressive saline environments.