Tailoring the dispersion of nanoparticles and the mechanical behavior of polymer nanocomposites by designing the chain architecture
GY Hou and W Tao and J Liu and YY Gao and LQ Zhang and Y Li, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19, 32024-32037 (2017).
The structure-property relationship of polymer nanocomposites (PNCs) has been extensively investigated, but less effort has been devoted to studying the effect of chain architectures. Herein, through coarse- grained molecular dynamics simulation, we build six different chain architectures namely linear, branch-2 (with two side chains), branch-4 (with four side chains), branch-10 (with ten side chains), star-4 (with four arms) and star-6 (with six arms), by fixing the molecular weight per chain. First, we examine the effect of the interfacial interaction between the polymer and nanoparticles (NPs) epsilon(np) on the dispersion of NPs, by calculating the radial distribution function between NPs, the second virial coefficient and the average number of neighbor fillers. We observe a non-monotonic change of the NP dispersion as a function of epsilon(np) for all PNCs with different chain architectures, indicating the optimal dispersion of NPs at moderate epsilon(np). Meanwhile, we find that the star-6, branch-4 and linear chains promote the best dispersion of NPs at moderate epsilon(np), compared to the other chain architectures. Then we investigate the strain hardening behavior and chain orientation of these PNCs under uniaxial tension. We find that the star-6 chains demonstrate relatively the most remarkable reinforced mechanical behavior of PNCs. Furthermore, we probe the effect of end-functionalization of polymer chains with different architectures on the dispersion of NPs, by comparing them to the case without any functionalization. We find that the introduction of the end-functionalization benefits mostly the high degree of chain branching for promoting the dispersion of NPs. Meanwhile, we observe that when the tensile strain is small, the branch-4 structure shows relatively improved mechanical properties, however, when the tensile strain is large, the star-6 and branch-10 structures display the best mechanical properties, and the end-functionalization evidently improves the mechanical properties of the PNCs. Our simulation results provide guidelines to tailor the dispersion of NPs and the mechanical properties of PNCs, by taking advantage of the chain architecture and its end- functionalization strategy.
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