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.