Shaping a Soft Future with Liquid Metal

Existing devices—such as cell phones, computers, and robots – are made from rigid materials, which is in direct contrast to the soft materials that compose the human body. In this talk, I willdiscuss several topics relate liquid metals within the context of creating devices (actuators, sensors, electronics) with tissue-like properties. Gallium-based liquid metals are often overlooked despite their remarkable properties: melting points below room temperature, water-like viscosity, low-toxicity, and effectively zero vapor pressure (they do not evaporate). Normally small volumes of liquids with large tension form spherical or hemi-spherical structures to minimize surface energy. Yet, these liquid metals can be patterned into non-spherical shapes (cones, wires, antennas) due to a thin, oxide skin that forms rapidly on its surface. Recently, we have discovered a simple way to separate the oxide from the metal as a way to deposit 2D-like oxides at ambient conditions. The process works by dragging a meniscus of liquid metal across a surface. At the right conditions, the fluid inside the meniscus is unstable and only oxide is left behind on the surface. Doing so enables direct-write printing of very thin (~3 nm) oxides without the need for vacuum processing. Surprisingly, the oxide is conductive because the printing process deposits a bilayer film inside which is a metallic-like layer. The ability to deposit oxide coatings is important for electronics, sensors, optics, and touch screens.