Electrical and rheological percolation of polymer nanocomposites prepared with functionalized copper nanowires.

The morphological, electrical and rheological characterization of polystyrene nanocomposites containing copper nanowires (CuNWs) functionalized with 1-octanethiol is presented. Characterization by SEM and TEM shows that surface functionalization of the nanowires resulted in significant dispersion of CuNWs in the PS matrix. The electrical characterization of the nanocomposites indicates that functionalized CuNWs start to form electrically conductive networks at lower concentrations (0.25 vol% Cu) than using unfunctionalized CuNWs (0.5 vol% Cu). The organic coating on the nanowires prevents significant changes in the electrical resistivity in the vicinity of the percolation threshold. Percolated nanocomposites showed electrical resistivity in the range of 10(6)-10(7) Ω cm. The transition from liquid-like to solid-like behavior (rheological percolation) of the nanocomposites was studied using dynamic rheology at 200 °C. Unfunctionalized CuNWs result in electrical and rheological percolation at similar concentrations. Functionalized CuNWs show rheological percolation at higher concentration (1.0-2.0 vol%) than that required for electrical percolation. This is attributed to the decrease in the interfacial tension between nanowires and polymer chains and its effect on the viscoelastic behavior of the combined polymer-nanowire networks.