Stretchable Liquid Metal Films with High Surface Area and Strain Invariant Resistance

This paper reports soft and stretchable films of liquid metal particles (LMPs) that offer high surface area and high conductivity. Liquid metals (LM) based on gallium are compelling conductors for soft and stretchable devices, yet it is difficult to make electrodes of LM with high surface area due to the tendency of liquids to minimize their surface area. To form films of percolated particles with high surface area, LMPs are first created by sonicating LM in isopropanol with trace amounts of hydrochloric acid and 1,6-hexane dithiol to decrease the amount of surface oxide on the LMPs. A film of these particles placed on a tacky substrate is initially insulating but percolate into conductive paths by straining the substrate. The resulting electrode has high conductivity (1.64 x 10(5) S m(-1)) and high surface area (1257% greater than a bulk LM film with the same areal footprint). Interestingly, these electrodes have nearly strain-invariant resistance (R/R-0 = 1.23 at 600% strain). The ability to create high surface area electrodes in such a simple manner may find use in sensing, capacitive storage, batteries, and energy-harvesting devices.