Ultrastretchable Fibers with Metallic Conductivity Using a Liquid Metal Alloy Core

Abstract

The fabrication and characterization of fibers that are ultrastretchable and have metallic electrical conductivity are described. The fibers consist of a liquid metal alloy, eutectic gallium indium (EGaIn), injected into the core of stretchable hollow fibers composed of a triblock copolymer, poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) resin. The hollow fibers are easy to mass‐produce with controlled size using commercially available melt processing methods. The fibers are similar to conventional metallic wires, but can be stretched orders of magnitude further while retaining electrical conductivity. Mechanical measurements with and without the liquid metal inside the fibers show the liquid core has a negligible impact on the mechanical properties of the fibers, which is in contrast to most conductive composite fibers. The fibers also maintain the same tactile properties with and without the metal. Electrical measurements show that the fibers increase resistance as the fiber elongates and the cross sectional area narrows. Fibers with larger diameters change from a triangular to a more circular cross‐section during stretching, which has the appeal of lowering the resistance below that predicted by theory. To demonstrate their utility, the ultrastretchable fibers are used as stretchable wires for earphones and for a battery charger and perform as well as their conventional parts.

Direct Writing of Gallium‐Indium Alloy for Stretchable Electronics

“…The resistance increase is roughly linear with strains up to 50%, with an approximate slope (gauge factor) of 1.5. However, resistance dependency deviates from the linear trend with strains greater than 50%, which is in agreement with previous studies …”

Monolithic fabrication of sensors and actuators in a soft robotic gripper

“…There is a high degree of repeatability in the results from both the uniaxial tests and the pneumatic actuation tests. The curve fit to the linear extension data is characteristic of uniaxial strain gauges and agrees with the literature [20], [24], [25], [26]. The pneumatic actuation data also increases monotonically, however, it does not display the quadratic response typical of uniaxial strain loading.…”

Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184

“…The elastomeric device stretches to larger strains without breaking, although there are some wrinkles on the surface of the metal that appear during stretching, as expected . The electrical properties of stretchable liquid metal conductors have been demonstrated previously. − We also fabricated stretchable devices using Elastosil-M4130 and M4630 (Figure S5). To prevent sticking of Elastosil-M4630 to the silicon mold, we cured it at room temperature.…”