The effect of single wall carbon nanotubes on the dipole orientation and piezoelectric properties of polymeric nanocomposites

Recently, a series of single wall carbon nanotube (SWNT) polyimide nanocomposites were developed since the demand of electroactive polymeric materials as sensors and actuators for use in high temperature applications has been growing. Adding SWNTs into electroactive polyimides enhanced their electrostrictive strain as well as their mechanical integrities and chemical stability. Although an increase in piezoelectricity resulting from the incorporation of SWNTs could be expected, there has been no systematic study detailing the effect of SWNTs on piezoelectricity. In this article, the effects of various types and concentrations of SWNT on the dipole orientation and piezoelectricity were investigated using a thermally stimulated current (TSC) technique and a modified Rheovibron. It was found that the barely modified SWNTs led to a more substantial increase in the remanent polarization (P-r) than the highly modified SWNTs did. As the loading level of SWNTs increased, P-r increased. However, excessive loading of SWNTs showed a reduction in P-r since the actual poling field decreased due to a large leakage of current. The trend of the piezoelectric strain coefficient, d(31), was consistent with that of P-r. The increase in interfacial polarization caused by adding SWNT was believed to be primarily responsible for the increase of P-r and d(31).