DEAs used in applications such as tunable lenses, soft robotics, etc. are expected to survive many thousands to millions of stretching cycles without degradation of their performance. Here, we present a measurement technique to characterise the evolution of the resistance of compliant electrodes submitted to cyclic biaxial strain, which represents the stretching configuration to which DEAs are usually submitted. We apply the novel electrode resistance degradation (NERD) method to the characterisation of compliant electrodes obtained by inkjet printing a carbon black suspension. We show that although the electrodes can sustain 1 million cycles of stretching at 5%, a 10% cyclic strain causes a much faster degradation, leading to a reduced actuation strain over time. We show that increasing the thickness of the electrodes leads to cracking and accelerated degradation; two layer electrodes degrade more rapidly than single layer electrodes. The NERD setup represents an efficient tool to quickly evaluate the suitability of different electrode formulations for use as compliant electrodes for DEAs.
Inkjet printing is an appealing technique to print electrodes for Dielectric Elastomer Actuators (DEAs). Here we present the preparation and ink-jet printing of a carbon black electrode mixture and characterise its properties. Carbon black has been used extensively in the past because it is very compliant; however, it has a high resistance and can be very dirty to work with. In this paper we show that carbon black remains an appropriate electrode material, and when inkjet printed can be used to fabricate devices meeting today’s demanding requirements. DEAs are becoming thinner to decrease actuation voltages and are shrinking in size to match the scale of the devices in the biomedical field, tuneable optics, and microfluidics. Inkjet printing addresses both of these problems. Firstly, Inkjet printing is a non-contact technique and can print on very thin freestanding membranes. Secondly, the high precision of inkjet printers makes it possible to print complex electrode geometries in the millimetre scale. We demonstrate the advantages of inkjet printing and carbon black electrodes by conducting a full characterisation of the printed electrodes. The printed carbon black electrodes have resistances as low as 13kΩ/□, an elastic modulus of approximately 1MPa, and a cyclic resistance swing which increases by 7% over 1500 cycles at 50% stretch. We also demonstrate a DEA with printed carbon black electrodes with a diametral stretch of 8.8% at an electric field of approximately 94V/μm. Finally a qualitative test is conducted to show that the printed carbon black electrode is extremely hardwearing.