Dynamic electro-mechanical analysis of highly conductive particle-elastomer composites

The availability of stretchable conductive materials is a key requirement for the development of soft and wearable electronics. Although there are many promising materials, the characterization of these materials under realistic conditions is complex and a standardized and reliable procedure has not been etablished yet. We therefore introduce a comprehensive protocol for the practice-oriented dynamic electro-mechanical analysis of elastomer-particle composites. In addition to strain dependence (0-100% strain) and fatigue strength (10,000 cycles), this protocol aims in particular to clarify the influence of strain rate (0-100% s-1) on conductivity. Samples with the commonly used filler representatives carbon black and silver flakes with 20 vol% each were prepared and investigated. Silicone elastomers of different stiffness were used as matrix in order to determine its influence. We found that while the conductivity of the carbon black composites of about 1 × 102 S m-1 proved to be fatigue resistant and largely independent of the strain rate, the silver flake composites lost their initially higher conductivity of 1 × 104 S m-1 at high strain rates and increasing numbers of cycles. In addition, the use of a softer silicone matrix improved the performance of both particle composites, which was also demonstrated on an exemplary wearable electronic device.