In this paper we present experimental measurements and analytical predictions for the electro-mechanical behaviour of Carbon Nanotube (CNT) actuators. Carbon nanotube actuators are chemo-electro- mechanical converters and exhibit very promising material parameters. To describe the electro-mechanical behavior, in the experimental part, some fundamental tests have been realized varying the voltage pattern while keeping the CNT materials, electrolyte, test configuration and other parameters unchanged. For out-of-plane deformation of the sheet material under applied voltage within a chemical environment, this analytical prediction is capable to show the voltage vs. active displacement behaviour for that material. Based on the experimental results from the different types of rectangular voltage pulses, we could successfully predict the material behaviour for triangular pulses. Finally based on these fundamental effects we are able to confirm the analytic prediction and to develop more sophisticated actuators.
Recent advances in technology have led to the development of nanostructured materials based on the assembly of carbon nanotubes with applications ranging from micromechanics to electronics and energy storage. An exciting property of carbon nanotubes is its electro-mechanical actuation behavior. The actuation behavior of the carbon nanotube paper (bucky paper) is greatly influenced by its surface resistance. In this work we propose to find out the resistance of the bucky paper, a porous meshwork of carbon nanotubes, automatically in a controlled and reproducible manner. The resistance is measured by using four wire resistance measurement instruments. It has two pairs of identical poles, positive and negative. Opposite polarity poles are short-circuited leading to two probes out of which one is taken as a reference and the other as varying probes. Considering multi walled carbon nanotube (MWNT) paper of 20 mm diameter, the reference probe is kept fixed at a single point and the varying probe is moved in different directions of the bucky paper plane. When performed manually the obtained results are highly nonlinear having many disturbances. In order to avoid these disturbances, an automatic movable probe holder has been designed and tested which provides a reproducible condition for the measurement automated by LabVIEW® interfacing. A direct measurement of resistance prior and later to the actuation testing is performed. Based on the results, the influence of resistance on actuation performance has been analyzed.
In this paper we present experimental measurements as well as a theoretical model for the chemo-electro-mechanical behavior of multi walled (MWNT) carbon nanotubes sheet actuators. Investigations of MWNT paper as an actuator and the analysis of the experimental and theoretical characteristics are special features of the presented work. The influencing parameters of the actuation behavior such as thickness of sheet materials and electrolyte concentration have been investigated. We report the experimentally measured active displacement varying quadratically with the applied electric field and non-linearly with the electrolyte concentration. In the theoretical part, we present a macroscopic actuation model for the global displacement behavior of MWNT materials. Finally, a comparison between the theoretical and the experimental investigations has been conducted.
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-characteristic can be optimized.
In conclusion, a good correlation between the experimental and the numerical results has been determined.