**Creep behavior of polymer nanocomposites: Insights from molecular
dynamics simulation**

ZC Chang and YF Wang and ZY Zhang and K Gao and GY Hou and JX Shen and LQ Zhang and J Liu, POLYMER, 228, 123895 (2021).

DOI: 10.1016/j.polymer.2021.123895

Creep behavior of polymer nanocomposites (PNCs) is a long-standing interesting topic, which is still lacking a molecular-level understanding. In this work, we employ coarse-grained molecular dynamics simulation to explore the effects of the filling fraction of the nanoparticles (NPs) and the interaction strength between polymer chains and NPs (epsilon np) on the creep performance of PNCs. We adopt the strain after a certain time under a constant force to quantitatively characterize the creep behavior. First, the effect of the filling fraction of NPs on the creep performance of PNCs was investigated. The results show that the addition of NPs significantly reduces the creep compliance of PNCs, attributed to the increase of the stiffness. Moreover, we found that as the filler volume fraction increases, the change of the creep strain can be roughly divided into three distinct stages, which is strongly related to the structure of the PNCs: the creep performance of PNCs increases with the increase of singlechain bridge structures (BB = 1) in the system. This special structure limits the slip of the matrix chain, thus enhancing the creep resistance of PNCs. Second, we also investigated the effect of the interaction between polymer chains and NPs (epsilon np) on the creep performance of PNCs. The creep resistance of PNCs increases with increasing epsilon np at the same filling fraction. This is due to the fact that the stronger the epsilon np, the tighter the combination between the molecular chains and the NPs. However, the incorporation of NPs will only benefit the creep resistance if the interfacial interaction is strong enough. This is because the slip of the polymer matrix chains is determined by a combination of the attractive forces between the matrix and the NPs, together with the repulsive forces between the NPs. We conclude that the incorporation of NPs leads to difficulty in sliding of the matrix chains only when the attraction between the molecular chains and NPs dominates. In general, we expect that our simulated results could provide some guidelines to rationally manipulate the creep mechanics of PNCs.

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