Synergies of Nanocopper\nand Graphene as Cofillers\nin a Shape-Memory Polyurethane

Graphene and its related materials are commonly used\nas reinforcements\nin shape-memory polymers (SMPs) to engineer their functional properties,\nbut at the cost of a reduction in their failure strain. Here, we demonstrate\nthat the reduced failure strain in multilayer graphene reinforced\npolyurethane (PU/MGR) composites (at 2.0 wt % MGR) could be enhanced\nby more than two times with the introduction of copper nanoparticle\n(CuNP) cofillers (0.1–1.0 wt % CuNP). The CuNPs play a crucial\nrole in disrupting the π–π and van der Waals interactions\nbetween the MGR sheets, which serve to reduce their agglomeration\nand suppress the number of stress–concentration sites. Interestingly,\nintroduction of CuNPs was found to not only increase the failure strain\nbut also contribute to remarkable tribological and thermal properties\nof the PU/MGR/CuNP composites. CuNP-decorated MGR fillers present\nat a sliding tribo-interface enabled the easy shearing and rolling\nof MGR sheets across each other, thereby significantly reducing the\nfriction to attain a state of superlubricity exhibiting an ultralow\nand stable coefficient of friction of ∼0.05–0.06. These\nconcepts derived from using CuNPs as cofillers in graphene-reinforced\nPU may be extended to many other SMP systems for various functional\nsystems.