Carbon nanotube and polyaniline composite actuators*

The actuation of a single-wall carbon nanotube (CNT) mat, an electrically conducting polyaniline (PAn) film and a composite of these two materials has been investigated in NaNO3 (1 M), NaCl (1 and 3 M) and HCl (1 M) solutions. The expansion and contraction patterns of the PAn, CNT and CNT/PAn samples are similar in these solutions. Fabrication of the CNT/PAn samples by coating PAn (CNT:PAn = 3:1 by weight) substantially enhanced the actuation strain (0.2–0.5%) of the CNT/PAn composite compared to the low actuation strain (0.06%) of the pure CNT mat. The actuation of PAn and CNT operates via different mechanisms. Non-Faradaic electrochemical charging of the CNT bundles is the main factor behind the expansion of CNT, while the expansion/contraction of PAn is dependent on the redox reactions of the polymer. The displacement pattern of the composite is dominated by the PAn component. However, when a load is applied to the sample (up to 1.2 MPa) the CNT/PAn sample behaves similarly to CNT samples, i.e. the actuation strain is almost independent of the applied loads in contrast to pure conducting polymers. This implies that the reinforcing effect of the CNT component is possibly due to the inherent high Young's modulus of the CNT bundles (∼640 GPa).