Influence of surface functionalization on the thermal and electrical properties of nanotube–PVA composites

We present an experimental study of the electrical and thermal properties of nanocomposites made of polyvinyl alcohol (PVA) and multiwall carbon nanotubes (CNTs). The CNTs are initially dispersed and stabilized in water by two methods: covalent acidic oxidation or by surfactant adsorption. The CNT dispersions are mixed with a PVA solution, filtered and dried to make composite materials. The resistivity of the composites decreases strongly with increasing the temperature for composites made of surfactant stabilized or oxidized-CNTs. However the rate of resistivity decrease differs substantially depending on the considered composites. This rate exhibits a maximum well above the glass transition of the neat PVA for oxidized-CNTs. This reflects strong interactions of oxidized-CNTs and the polymer confined at the CNT interfaces. By contrast, surfactant stabilized CNTs exhibit weaker interactions and the maximum of resistivity decrease occurs at the glass transition temperature of the neat PVA. The present results show the critical importance of covalent or non-covalent surface functionalization for the conductive properties of nanocomposites. The latter are affected by modification of the thermal properties of the polymer through either the presence of additives in bulk or confinement and strong interactions at the CNT interfaces.