Thermo-Mechanically Stable, Liquid Metal Embedded Soft Materials for High-Temperature Applications

Liquid-metal embedded elastomers (LMEEs) have been demonstrated to show a variety of excellent properties, including high toughness, dielectric constant, and thermal conductivity, with applications across soft electronics and robotics. However, within this scope of use cases, operation in extreme environments - such as high-temperature conditions - may lead to material degradation. While prior works highlight the functionality of LMEEs, there is limited insight on the thermal stability of these soft materials and how the effects of liquid metal (LM) inclusions depend on temperature. Here, the effects on thermal stability, including mechanical and electrical properties, of LMEEs are introduced. Effects are characterized for both fluoroelastomer and other elastomer-based composites at temperature exposures up to 325 degrees C, where it is shown that embedding LM can offer improvements in thermo-mechanical stability. Compared to elastomer like silicone rubber that has been previously used for LMEEs, a fluoroelastomer matrix offers a higher dielectric constant and significant improvement in thermo-mechanical stability without sacrificing room temperature properties, such as thermal conductivity and modulus. Fluoroelastomer-LM composites offer a promising soft, multi-functional material for high-temperature applications, which is demonstrated here with a printed, soft heat sink and an endoscopic sensor capable of wireless sensing of high temperatures. The thermo-mechanical stability of liquid metal-elastomer composites are studied and liquid metal is shown to enhance thermo-mechanical stability by toughening soft materials at high temperatures. A highly thermally stable composite is introduced where the material maintains rubber-like properties up to 325 degrees C. These thermally stable, multi-functional materials may enable soft robotics for extreme environments, including in high-temperature conditions and space applications.image