Electro-mechanical behavior of carbon nanotube sheets in electrochemical actuators

There is considerable need for light, low-volume actuators having long-cycle-life that can generate large displacements and high forces when low voltages are applied. Electroactive polymers (such as piezoelectric and electrostrictive polymers, polyelectrolyte gels, and conducting polymers) possess some of these characteristics, but improvements are needed. We describe work on a promising new type of actuator that is 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. The present work describes recent advances in increasing the actuator stroke and stress generation capabilities well above our initially obtained values for carbon nanotube actuators. Operating these actuators in IM 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.