Asymmetric Interfacial Chain Diffusion in High-Performance Thermoplastics

Adhesion technologies between high-performance thermoplastics have attracted growing attention for weight reduction in mobility applications and improved manufacturing productivity. The adhesion interface is formed via polymer chain interdiffusion, and the resulting interfacial structure governs adhesion properties. Thus, understanding the interfacial aggregation states is essential. Here, we examined the chemical composition distribution at the adhesion interface between poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) adhered at various temperatures to clarify the chain diffusion behavior. Raman scattering spectroscopy was performed along the direction perpendicular to the adhesion interface, enabling evaluation of chemical composition distributions based on the characteristic carbonyl peak intensities. The obtained profiles exhibited asymmetric spreading toward the PEEK side, indicating higher chain mobility of PEEK than PEI. The results were analyzed based on the diffusion equation to calculate interdiffusion coefficients, which markedly increased above the melting temperature of PEEK. These findings suggest that complete melting of PEEK crystals significantly enhances interfacial chain diffusion.