Novel Testing Method of Carbon Nanotube-Array Actuators

Abstract

Mats of randomly oriented carbon nanotubes, known as Bucky papers, show in contact with an ionic electrolyte an active strain based on the capacitor-like mode of operation. The mats are manufactured by a filtration of an aqueous dispersion. The dispersion is made of commercially available CNT-powder. Various investigations show low reliability and reproducibility of powder-based structures because of the low powder-quality. Furthermore the random orientation of the papers does not allow using the excellent properties of a single CNT. That is the reason why great efforts are made to align the free movable CNTs in the dispersion. Other aligned CNT-based struc-tures like yarns or CNT-array-based papers suffer from low conductibility, low stiffness or bad a-lignment according to the manufacturing process. The mechanism of strain generation still remains undefined but there is a controversial discussion. Either it is a quantum-mechanical lengthening of C-bonds or an electrostatic repulsion between charged CNTs. Maybe it is a superposition of both mechanisms. The presented paper focuses on a method for measuring the free strain of as pro-duced vertically aligned CNT-arrays. This presented test set-up, the way of analysis and the used specimen avoid on the one hand measuring secondary effects and allow on the other hand re-cording the reaction of one MWCNT standing in parallel as an array. Therefore the analysed effect must be dominated by a quantum-mechanical character.