(649b) Expanding the Formulation Boundaries for Soft, Stretchable Liquid Metal Composites

Stretchable electronics have increasingly been proven to provide exceptional performance, particularly as sensors, robotic components, and wearable technology. While the applications for stretchable electronics expand, there is still a great need for materials that have optimal electronic performance while remaining soft and stretchable. Many materials have been proposed and composites of polymers, specifically elastomers such as silicones and block copolymer thermoplastics, and conductive materials stand out as one of the most easily manufactured and precisely engineered options. In particular, composites of elastomers and room-temperature liquid metals such as the gallium-based eutectic alloys gallium-indium-tin, Galinstan, and gallium-indium, eGaIn, have been shown to have a low impact on the host elastomer modulus while achieving dielectric constants above 100. While previous work has shown this electronic behavior is possible, the presented work investigates the dielectric loss associated with these materials. As the concentration of metal required to achieve a high dielectric constant is significant (70vol% of liquid metal or higher), the resultant dielectric loss is high. To combat this, novel formulations for liquid metal composites were investigated, incorporating rigid materials with independently high electrical behavior to maximize the potential of the liquid metal composites as components of stretchable capacitors. In order to optimize the composite as a sensor, the modulus of the composite material alone was measured in torsion, tension, and compression achieving modulus values spanning over three orders of magnitude. This was done in parallel with impedance analysis of the new composites, determining the dielectric constant and dielectric loss associated with each material. By expanding the possible formulation space of stretchable, dielectric, liquid metal-based composites, new sensors with improved sensitivity and maximal load can be tailored to specific applications.