Carbon Nanotube Sheet Actuators

In the latest period, several materials have been proposed to realize light, low-volume actuators having long-cycle life that can generate large displacements and high forces when voltages are applied. Electroactive polymers (such as piezoelectric polymers, polyelectrolyte gels, conducting polymers and, recently, carbon nanotubes) have some of these characteristics, in particular the last type. The nanotube sheet actuators are based on non-faradaic electrochemical charge injection in carbon nanotube sheets. While large actuator strokes combined with giant stress generation capabilities are predicted for optimized materials, the present stage of actuator development is embryonic and major materials advances are required to realize these features. Operating these actuators in 1M NaCl at low voltages (-0.5 to 1.5 V vs. SCE) we obtained actuator strain of up to 1%. Although the generated stresses (up to 1.5 MPa) are much higher than those of natural muscles, they are many orders of magnitude lower than predicted for nanotube sheets that fully utilize the mechanical properties of the individual nanotubes.