Chemical functionalities govern polyamide–alumina adhesion through local conformational dynamics

Abstract Direct bonding of polyamides (PAs) to metals is crucial for lightweight structural applications, yet the molecular mechanisms governing bonding strength remain elusive. Here, we present all-atom molecular dynamics simulations of PAs bonded to alumina under tensile strain. Introducing a segmental-scale structural descriptor, the local radius of gyration, to quantify conformational changes in adsorbed chains, we reveal three distinct conformational modes—tail elongation, loop-to-tail transition, and chain desorption. In the elastic regime, the tensile stress is determined by PA chemistry: aromatic PAMXD6 resists deformation better than aliphatic PA6. After yielding, the alumina surface termination becomes critical. PAMXD6 chains desorb from OH-terminated surfaces, whereas PA6 chains exhibit localized conformational rearrangements through loop-to-tail transitions. In contrast, both PA6 and PAMXD6 chains on non-terminated surfaces retain adhesion via rigid trains and loops. These findings reveal how chemical functionalities govern conformational dynamics and ultimately adhesion strength, offering general design principles for robust polymer–inorganic hybrid materials.