Fabrication and Characterization of Transparent Stretchable Electrodes

Optical visualisation of cells under mechanical stimulation is challenging outside the human body, particularly when using dielectric elastomer actuators (DEAs). These devices, whilst composed of transparent films (dielectric layer), have electrodes that remain opaque, rendering them unsuitable for optical measurements such as microscopy. In this project, we aim to establish transparent, stretchable electrodes for fully transparent DEAs. Due to their high transmittance, low resistivity, and low Young’s modulus, carbon nanotubes (CNTs) are used as the electrode material. Different CNT area densities are employed during electrode layer fabrication to evaluate their effects on resistance, transmittance, and stiffness. Carbon black (CB) electrodes, normally used for DEAs, are also characterised and compared with the novel CNT electrodes. From the results, the overall sheet resistance of CNT electrodes (1.04 M Ω/sq for 0.27 g/cm2) was approximately 3 times lower than that of CB electrodes (3.14 M Ω/sq). In addition, the sheet resistance decreased further with increasing CNT layer area density. The piezoresistive effect in carbon black electrodes varied, whereas it remained constant in CNT electrodes throughout the deload-load cycles. For both electrode materials, the influence on the stiffness is small. Lastly, the CNT electrodes achieved a transmission of 98.9% at 700 nm. Compared with carbon black electrodes, CNT electrodes provide an efficient, transparent, and stretchable alternative to current DEA technology for optical analysis of cellular behaviour in muscle-like environments, without reducing resistance or increasing stiffness.