Nanosecond laser -assisted coating of epoxy/MWCNT on thermoplastic polymer: Influence on morphology, defect healing, and thermal-mechanical enhancement

The development of high-performance, flexible conductive coating with enhanced electrical conductivity, thermal stability, and mechanical durability remains a critical challenge in advanced materials and coating technologies. This study investigates the effect of nanosecond laser scanning line spacing on the structural, morphological, thermal, mechanical, and electrical properties of epoxy/multiwalled carbon nanotube (Ep–MWCNT) coatings deposited on polyethylene terephthalate (PET) substrates. Raman analysis revealed a non-linear defect evolution, with the lowest defect density (I_D/I_G = 0.623) achieved at an optimal line spacing of 4 μm, indicating effective defect healing and enhanced graphitic ordering. SEM and HR-TEM observations confirmed improved nanotube alignment, interconnectivity, and stronger interfacial bonding after laser irradiation, while excessive spacing led to nanotube agglomeration and structural degradation. XRD results demonstrated increased crystallinity and graphitization, evidenced by a sharp (002) peak at 26° in laser-treated samples. Thermogravimetric analysis showed a remarkable enhancement in thermal stability, with the maximum degradation temperature shifting from 456 °C (pure PET) to 852 °C (after laser treatment of Ep-MWCNT/PET composite. Dynamic mechanical analysis revealed significant improvements in storage modulus and reduced damping behavior, indicating enhanced stiffness and interfacial constraint. Electrically, the optimized coating (4 μm) exhibited the lowest sheet resistance 218 Ω/sq. and improved bending stability, with consistent cyclic sensing performance and reduced signal fluctuation. Furthermore, laser processing enhanced flexural strength and promoted dense, uniform morphology after repeated bending. FTIR analysis confirmed laser-induced chemical modifications and stronger matrix–nanotube interactions. Taken together, nanosecond laser tuning provides an effective strategy for defect healing, network optimization, and multifunctional performance enhancement of Ep–MWCNT coatings on flexible PET substrates for advanced organic coating and flexible electronic applications.