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Electrical permittivity has a central role in the performance of a wide range of dielectric elastomer technologies, from electrostatically-controlled actuators to capacitive sensors and energy harvesting transducers. One approach to improving the permittivity of elastomers is to create an “artificial dielectric” by adding metal filler. However, the addition of rigid filler can reduce the mechanical compliance and elasticity of the host elastomer and result in decreased electromechanical coupling. To avoid this trade-off, I introduce an alternative approach in which the rigid filler is replaced with a dispersion of droplets of liquid-phase metal alloy. Using eutectic gallium-indium (EGaIn) as the liquid metal, I show that it is possible to engineer artificial dielectrics that preserve the mechanical properties of the host elastomer. Moreover, significant degradation of the elastomer’s electrical breakdown strength can be avoided through control of the droplet size and polydispersity. After a discussion of the underlying principles for permittivity enhancement, I present approaches to theoretical methoding based on effective medium approximations and homogenization theories that are in reasonable agreement with the experimental measurements. To demonstrate the practical use of these EGaIn-elastomer composites in dielectric applications, I briefly review three use cases. The first is a capacitive sensor with EGaIn electrodes that measures stretch as a function of change in capacitance. The second is a flexural dielectric elastomer actuator that shows a 80% improvement in blocking force compared to elastomers without EGaIn filler. In the third example, I present a dielectric energy harvesting system that generates significantly more electrostatic energy when EGaIn filler is added to the dielectric.
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