Carbon-nanotube-sheet actuator - theoretical and experimental investigations

In this paper we present experimental measurements as well as a theoretical model for the electro-mechanical behavior of single walled carbon nanotube (SWNT) sheet actuators. The SWNT material exhibits elongation and contraction of the carbon bond length due to electro-chemically induced surface charge and works at a relatively low operating voltage. The use of carbon nanotube sheet material sandwich with porous ceramic is a special feature of the presented work. In the experiment, two layers of SWNT with a ceramic layer in between were placed between two working-electrodes in an electrolyte solution bath. The counter electrode has been placed within the solution away from the composite. The charge transfer takes place between the working and the counter electrodes. The displacement of the composite was measured in the thickness direction, i.e. between the fixed and the mobile working electrodes. Depending on the applied voltage, different displacement values up to 0.8% of its original thickness were obtained. As influencing factors, the parameters such as applied electric field, thickness of the composite, solvent and electrode type were investigated. A clear dependency of the actuation on the applied potential was observed within the electro-chemical window. It is remarkable that an applied electric voltage exceeding the window leads to a hydrolysis of the solvent, i.e. generation of gas bubbles. In the theoretical part, a macroscopic model for the actuation of the SWNT material has been developed. A mechanical field equation which uses the applied electric potential as input gives the elongation and contraction of the material. Depending on the parameters given above, the time-behavior of the actuator has been simulated. Thus, by various numerical simulations and experimental investigations, the actuator-characteristics can be optimized. In conclusion, a good corelation between the experimental and the numerical results has been determined.