Multifunctional epoxy nanocomposites incorporating silanised bismuth ferrite and PDA-modified PANI/rGO for enhanced corrosion protection, piezoelectric early warning, shape-memory assisted crack closure, and flame retardancy

Metallic corrosion and structural degradation threaten offshore wind towers exposed to salt spray, mechanical damage, and fire. This study develops a lead-free multifunctional epoxy nanocomposite coating that integrates active corrosion protection, piezoelectric damage sensing, near-infrared (NIR)-triggered shape-memory crack closure, and flame retardancy within a single system. To achieve uniform filler dispersion, bismuth ferrite (BFO) nanoparticles were functionalised with 3-aminopropyltriethoxysilane (APTES), while reduced graphene oxide (rGO) was modified with polydopamine (PDA) followed by in situ polymerisation of polyaniline (PANI), producing a homogeneous 0–3 architecture. The coating exhibited enhanced thermal and mechanical performance, with a glass transition temperature of 105°C and adhesion strength of 9.9 MPa. The embedded BFO generated a stable 14.3 V peak-to-peak piezoelectric output for damage sensing. Under 808 nm NIR irradiation (1.0 W/cm2), the PDA-PANI/rGO network rapidly heated to 150°C, enabling shape-memory-assisted crack closure and restoring 90% of the original barrier impedance after three healing cycles. The coating maintained a resistance of 4.13 × 109 Ω·cm2 after 28 days in saline, reduced corrosion current to 5.01 × 10−7 A/cm2, and achieved a 61% reduction in peak heat release with UL-94 V-0 and an LOI of 32.5%, demonstrating exceptional multifunctional protection for marine infrastructure.