Molecular Dynamics Simulations of Polymer Nanocomposites Welding: Interfacial Structure, Dynamics and Strength

Polymer welding has received numerous scientific attention, however, the welding of polymer nanocomposites (PNCs) has not been studied yet. In this work, via coarse-grained molecular dynamics simulation, the attention on investigating the welding interfacial structure, dynamics, and strength by constructing the upper and lower layers of PNCs, by varying the polymer–nanoparticle (NP) interaction strength ε_NP-p is focused. Remarkably, at low ε_NP-p, the NPs gradually migrate into the top and bottom surface layer perpendicular to the z direction during the adhesion process, while they are distributed in the middle region at high ε_NP-p. Meanwhile, the dimension of polymer chains is found to exhibit a remarkable anisotropy evidenced by the root-mean-square radius of gyration in the xy- (R_g,xy) and z- (R_g,z) component. The welding interdiffusion depth increases the fastest at low ε_NP-p, attributed to the high mobility of polymer chains and NPs. Lastly, although the mechanical properties of PNCs at high ε_NP-p is the strongest because of the presence of the NPs in the bulk region, the welding efficiency is the greatest at low ε_NP-p. Generally, this work provides a fundamental understanding of the interfacial welding of PNCs, in hopes of guiding to design and fabricate excellent self-healable PNCs.