Electrostrictive thermoplastic polyurethane-based nanocomposites filled with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH): Properties and improvement of electromechanical activity

摘要

The impact of small amounts of carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) added into a polyether-based thermoplastic polyurethane elastomer (TPU) was studied considering mainly on the morphological, mechanical, electrical and electrostrictive properties. The electrostrictive properties were measured by the analysis of the deformation response occurring under external electric fields £ applied on 50 μm-thick films. Dielectric measurements were carried out in order to determine the percolation threshold f_c,, which was found near 1 v% loading. This volume fraction leads to a very high dielectric permittivity ε_r~' up to ≈330, i.e. about 50 times higher than that of the pure TPU, where ε_r~' ≈ 6-7. The thickness strain S_Z and apparent electrostrictive coefficient M were measured at low electric fields, E ≤ 4 V/μm, by low frequency of 0.1 Hz. The maximum induced-compressive strain was obtained from an optimal volume fraction of 0.8 v% which yielded to a high S_z = -11.5% corresponding to almost a threefold increase of M compared to the neat TPU. Beyond f_c, the conductivity sharply raised up and thus the electrostrictive activity disappeared.