Theoretical versus experimental performance transfer analysis of multiple carbon nanotube actuator systems

Carbon nanotube (CNT) - polymer actuators were developed as the follow-up of Bucky Papers allowing the operation of those structures at room conditions and most importantly without the need of immersing them in electrolyte bath. This development step has brought CNT actuator technology closer to the phase of application development. Previously the necessity of the liquid electrolyte restricted those activities due to the need for complicated system design with high, weight and volume as well as cumbersome maintenance and high costs. CNT - polymer actuators are constructed as three layers structures and operate under low applied voltages (2 Volt) and at low frequencies <1 Hz) in an out-of-plane mode. Performance of those actuators with respect to displacement and generated force have shown a great improvement over the last few years reaching values of 5,8 % and up to 15 N, respectively. However, it was also shown that those two performance features are not proportional, meaning that influencing one of them would adversely affect the other. In order to be able to offer a CNT actuator with both improved displacement as weIl as improved force exertion several approaches were investigated. Attempts of improving actuators performance by increase of CNT content in polymer matrix or by increase of active layer thickness proved to be inefficient due to the negative influence on the material properties and charge transfer, respectively. For this reason, multiple actuator systems were designed; by this one should understand a system composed of several three layer actuators stacked one on another with a suitable design of electrodes in between of them. It was predicted that by such design the performance of the resulting system will be a summation of separate actuator performances 01' in a case of perfect reproducibility of actuator the performance of multiple system will be a multiplication of single actuator performance by the number of actuators used. The experimental investigations, however, have shown that the improvement of the system performance is not directly proportional to the increase in number of actuators and thus, does not follow the theoretical predictions. As a result of this research work the experimental results of the performance, displacement and force, of multiple actuator systems are plotted against the theoretically estimated values. Explanation of the lack of proportionality in the improvement is given from the point of view of reproducibility of actuators, electrodes design for the system as weIl as handling issues. The attempt is taken to find the performance relations that would allow in the future the design and construction of multiple carbon nanotube actuator systems with predictable and reproducible performance.