Self-Running Liquid Metal Drops that Delaminate Metal Films at Record Velocities

Abstract

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 ∼100 nm thick, ∼ 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.

Liquid Metal–Based Soft Microfluidics

“…b) Schematics and photographs showing an electric circuit self‐destroyed by a liquid metal droplet via delaminating the solid metal underneath. Reproduced with permission . Copyright 2015, American Chemical Society.…”

Wiring up Liquid Metal: Stable and Robust Electrical Contacts Enabled by Printable Graphene Inks

“…In a recent dramatic demonstration of this effect, Dickey and coworkers exploited the aggressive alloying of eGaIn with silver to direct the motion of liquid metal droplets across a surface, completely removing the silver in the process. [24] Therefore, to enable broader application of eGaIn with conventional circuits, interfacial alloying needs to be suppressed without compromising electrical or mechanical properties.Here, we demonstrate printed graphene as a reliable and high-performance interfacial layer to enable electrical connections to eGaIn. In contrast to conventional metals, sp 2 -bonded carbon materials are stable to alloy formation with liquid metals.…”

“…In a recent dramatic demonstration of this effect, Dickey and coworkers exploited the aggressive alloying of eGaIn with silver to direct the motion of liquid metal droplets across a surface, completely removing the silver in the process. [24] Therefore, to enable broader application of eGaIn with conventional circuits, interfacial alloying needs to be suppressed without compromising electrical or mechanical properties.…”

“…This configuration exhibits clear alloying between the silver and eGaIn, as expected from prior reports. [4,24] To establish the ability of graphene to stabilize this interface, a similar sample is fabricated with a thin film (≈100 nm) of graphene printed between the silver and eGaIn. The graphene ink and printing methods are adopted from recent work, [30] resulting in a continuous film of few-layer graphene flakes with a dense microstructure, functioning as a physical barrier between the eGaIn and silver (Figures S1 and S2, Supporting Information).…”

Ga-Based Alloys in Microelectronic Interconnects: A Review

“…These includes basic thermophysical [11,21,34,44,45,73,74], electrochemical [46,75,76,77], electromagnetic [78,79], fluidity and wettability properties [80,81,82], and self-fueled actuation, in which chemical energy spontaneously converts into mechanical activity to induce autonomous locomotion [77,83,84]. These research achievements lay the foundation for some techniques for liquid alloy control and utilisation, such as patterning the deposit liquid metal [7,85,86] and fabricating small liquid metal particles [87,88,89].…”