Single walled carbon nanotube (SWNT)–polyimide nanocomposites as electrostrictive materials

The combination of properties offered by polymer nanocomposites provides opportunities for going beyond structural reinforcement where engineered electroactive responses and enhanced electrical and dielectric properties would result in multifunctionality. In our study, we show that adding single walled carbon nanotubes (SWNTs) to a non-actuating polyimide (PI) can create an electromechanical actuation response in the nanocomposite. The neat polyimide does not show any actuation response under an applied electric field, whereas the SWNT–PI composites above the percolation threshold exhibit an electrostrictive behavior that is highly dependent on SWNT content. Both bending and thickness–extension strains are obtained at very low electric field magnitudes; the study also evaluates the effect of applied electric field magnitude, frequency and SWNT content on the actuation strain and strain rate. Dielectric spectroscopy and thermally stimulated current measurements reveal an enhanced polarization in the presence of SWNTs. This enhancement is key to the actuation mechanism and is thought to arise from a combination of three sources: SWNTs acting as extended electrodes within the polymer, interfacial polarization and noncovalent interactions between the SWNTs and the polymer.