Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 7, Issue 41, Pages 23163-23171Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.5b06978
Keywords
liquid metal; EGaIn; self-running; metal films; film delamination; transient electronics
Funding
- NSF [CMMI-0954321, CMMI-1362284]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1362284, 954321] Funding Source: National Science Foundation
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This paper describes a new method to spontaneously accelerate droplets of liquid metal (eutectic gallium indium, EGaIn) to extremely fast velocities through a liquid medium and along predefined metallic paths. The droplet wets a thin metal trace (a film similar to 100 nm thick, similar to 1 mm wide) and generates a force that simultaneously delaminates the trace from the substrate (enhanced by spontaneous electrochemical reactions) while accelerating the droplet along the trace. The formation of a surface oxide on EGaIn prevents it from moving, but the use of an acidic medium or application of a reducing bias to the trace continuously removes the oxide skin to enable motion. The trace ultimately provides a sacrificial pathway for the metal and provides a mm-scale mimic to the templates used to guide molecular motors found in biology (e.g., actin filaments). The liquid metal can accelerate along linear, curved and U-shaped traces as well as uphill on surfaces inclined by 30 degrees. The droplets can accelerate through a viscous medium up to 180 mm/sec which is almost double the highest reported speed for self-running liquid metal droplets. The actuation of microscale objects found in nature (e.g., cells, microorganisms) inspires new mechanisms, such as these, to manipulate small objects. Droplets that are metallic may find additional applications in reconfigurable circuits, optics, heat transfer elements, and transient electronic circuits; the paper demonstrates the latter.
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