Soft Electronics and Sensors Using Liquid Metals

This talk will discuss the use of liquid metals as conductors for soft and stretchable electronics and devices. Alloys of gallium are noted for their low viscosity, low toxicity, and near-zero vapor pressure. Despite the large surface tension of the metal, it can be patterned into non-spherical 2D and 3D shapes due to the presence of an ultra-thin oxide skin that forms on its surface. Because it is a liquid, it can be patterned in ways that are truly unique for metals, such as printing, injection, and selective wetting. The metal is extremely soft and flows in response to stress to retain electrical continuity under extreme deformation. By embedding the metal into elastomeric or gel substrates, it is possible to form soft, flexible, and conformal electrical components, stretchable antennas, and ultra-stretchable wires that maintain metallic conductivity up to ~800% strain. In addition to discussing the advantages of these materials for electronics, this talk will focus on recent work to utilize liquid metal for tactile sensors. The sensors detect touch from changes in capacitance. By using soft composites consisting of liquid metal particles dispersed in elastomer, it is possible to increase the dielectric properties while using ultra-soft materials. Thus, the sensors are very sensitive to touch. Furthermore, liquid metals can be utilized as an important part of a process to treat surfaces to render them antibacterial and antiviral, which is particularly useful for healthcare applications. Specifically, we show that liquid metal particles can stick to fibers and serve as a source for deposition of copper via redox reactions. The resulting coating has excellent adhesion to the fibers and provides antibacterial and antiviral properties. Combined, these advances have exciting implications for soft devices for stretchable electronics and wearables.