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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.

Although never emphasized and increasingly used in organic electronics, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) layer-by-layer (lbl) film construction violates the alternation of polyanion and polycation rule stated as a prerequisit for a step-by-step film buildup. To demonstrate that this alternation is not always necessary, we studied the step-by-step construction of films using a single solution containing polycation/polyanion complexes. We investigated four different systems: PEDOT-PSS, bPEI-PSS (branched poly(ethylene imine)-poly(sodium 4-styrene sulfonate)), PDADMA-PSS (poly(diallyl dimethyl ammonium)-PSS), and PAH-PSS (poly(allylamine hydrochloride)-PSS). The film buildup obtained by spin-coating or dipping-and-drying process was monitored by ellipsometry, UV-vis-NIR spectrophotometry, and quartz-crystal microbalance. The surface morphology of the films was characterized by atomic force microscopy in tapping mode. After an initial transient regime, the different films have a linear buildup with the number of deposition steps. It appears that, when the particles composed of polyanion-polycation complex and complex aggregates in solution are more or less liquid (case of PEDOT-PSS and bPEI-PSS), our method leads to smooth films (roughness on the order of 1-2 nm). On the other hand, when these complexes are more or less solid particles (case of PDADMA-PSS and PAH-PSS), the resulting films are much rougher (typically 10 nm). Polycation/polyanion molar ratios in monomer unit of the liquid, rinsing, and drying steps are key parameters governing the film buildup process with an optimal polycation/polyanion molar ratio leading to the fastest film growth. This new and general lbl method, designated as 2-in-1 method, allows obtaining regular and controlled film buildup with a single liquid containing polyelectrolyte complexes and opens a new route for surface functionalization with polyelectrolytes. journal article research support, non-u.s. gov't 2012 Jun 12 2012 05 31 imported

We present an automated system to measure the degradation of compliant electrodes used in dielectric elastomer actuators (DEAs) over millions of cycles. Electrodes for DEAs generally experience biaxial linear strains of more than 10%. The decrease in electrode conductivity induced by this repeated fast mechanical deformation impacts the bandwidth of the actuator and its strain homogeneity. Changes in the electrode mechanical properties lead to reduced actuation strain. Rather than using an external actuator to periodically deform the electrodes, our measurement method consists of measuring the properties of an electrode in an expanding circle DEA. A programmable high voltage power supply drives the actuator with a square signal up to 1 kHz, periodically actuating the DEA, and thus stretching the electrodes. The DEA strain is monitored with a universal serial bus camera, while the resistance of the ground electrode is measured with a multimeter. The system can be used for any type of electrode. We validated the test setup by characterising a carbon black/silicone composite that we commonly use as compliant electrode. Although the composite is well-suited for tens of millions of cycles of actuation below 5%, we observe important degradation for higher deformations. When activated at a 20% radial strain, the electrodes suffer from important damage after a few thousand cycles, and an inhomogeneous actuation is observed, with the strain localised in a sub-region of the actuator only.

We report on the integration of a dielectric elastomer actuator (DEA) operating at 1 kV with a flexible metal oxide high-voltage thin film transistor (HVTFT). With only a 30 V gate voltage, the HVTFT controls the kV voltage drop across the DEA, thus providing low-voltage control over the DEA actuation. Both the DEA and the HVTFT are stable up to over 105 cycles. This integrated DEA+HVTFT actuation strategy represents a key building block for smart complex compliant machines, for which multiple independent soft actuators are required. An array of many such building blocks can be driven by a single DC kV power supply, with each DEA individually addressed with low-voltage signal outputs, for example in a row/column architecture. Since the switching logic now operates at low voltage, one can integrate high-level control in multi degree of freedom soft DEA robots.