Field-Controlled Electrical Switch with Liquid Metal.

James Wissman,Michael D Dickey,Carmel Majidi

doi:10.1002/advs.201700169

Abstract

When immersed in an electrolyte, droplets of Ga‐based liquid metal (LM) alloy can be manipulated in ways not possible with conventional electrocapillarity or electrowetting. This study demonstrates how LM electrochemistry can be exploited to coalesce and separate droplets under moderate voltages of ~1–10 V. This novel approach to droplet interaction can be explained with a theory that accounts for oxidation and reduction as well as fluidic instabilities. Based on simulations and experimental analysis, this study finds that droplet separation is governed by a unique limit‐point instability that arises from gradients in bipolar electrochemical reactions that lead to gradients in interfacial tension. The LM coalescence and separation are used to create a field‐programmable electrical switch. As with conventional relays or flip‐flop latch circuits, the system can transition between bistable (separated or coalesced) states, making it useful for memory storage, logic, and shape‐programmable circuitry using entirely liquids instead of solid‐state materials.

Highlights

The analysis suggests that the kinetics of oxide growth/ removal and droplet motion are influenced by geometry (V, s, D), electrical stimulation (Φ, I), and the electrolytic concentration
We present a fluidic electrical switch that reversibly changes its electrical conductivity by three orders of magnitude in response to moderate applied voltage (1–10 V)
LM droplet separation is controlled by a novel fluidic instability that is driven by a field-controlled gradient in interfacial tension and has not before observed in fluidic electrowetting or LM droplet manipulation

Summary

Introduction

1. Introduction sistors, on/off states can be manipulated with the input of electric fields, and a gate–source threshold voltage must be Coalescence and separation of liquid droplets are typically gov- met to achieve off-to-on switching (coalescence). Further demonstration of switching and details the reversible coalescence and separation of liquid droplets regarding functionality are reported in Video S1 and in the conthrough electrowetting or electrochemistry under voltages tent of the Supporting Information. The LM is a eutectic Ga–In (EGaIn) alloy, which forms a microfluidics that can be directly operated with conventional Ga2O3 surface oxide in aqueous basic environments when microelectronics and power supplies. It provides an placed under an oxidative potential. When such a potential is opportunity to further explore the interplay between interfacial applied directly to the source electrode (relative to the gate), the associated LM spreads, contacts, and coalescences with the

Results

Discussion

Conclusion