Giant and switchable surface activity of liquid metal via surface oxidation

Khan, M. Rashed; Eaker, Collin B.; Bowden, Edmond F.; Dickey, Michael D.

doi:10.1073/pnas.1412227111

Cited by 345 publications

(425 citation statements)

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“…When immersed in a 1 m NaOH(aq) solution, voltage‐controlled (<10 V) oxidation leads to a dramatic decrease in effective interfacial tension 13. Under gravity, the droplet will flatten, which we harness here to bring the droplets closer together and ultimately coalesce.…”

Section: Introductionmentioning

confidence: 99%

Field‐Controlled Electrical Switch with Liquid Metal

2017

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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.

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Section: Introductionmentioning

confidence: 99%

Field‐Controlled Electrical Switch with Liquid Metal

2017

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“…The shapes formed in the region above the critical potential are still being investigated but are attributed to the surface tension being near zero. Details can be found in the literature 1 .…”

Section: Discussionmentioning

confidence: 99%

“…The method uses modest voltages (~1 V) applied directly to the liquid metal (relative to a counter electrode in the presence of electrolyte) to achieve enormous and reversible changes to the surface tension of the metal 1 .…”

Section: Introductionmentioning

confidence: 99%

“…This delta change in surface tension may be the largest ever reported in literature for any fluid and it can be accomplished in a tunable and reversible manner. These large changes in surface tension are useful for manipulating the capillary behavior of metals; for example, it can induce the metal to spread on a surface, withdraw the metal from microchannels, fill microchannels with metal, and overcome the Rayleigh instabilities to form liquid metal fibers 1,21 .…”

Section: Introductionmentioning

confidence: 99%

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A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Eaker

Khan

Dickey

2016

JoVE

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Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( ̴ 500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests. Video LinkThe video component of this article can be found at

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“…Alternatively, the liquid metal can be immersed in a strong acid or base [49,50], which chemically reduces the oxide layer and prevents it from reforming. The use of electrolytic carrier fluids also allows for surface-tension-based actuation techniques [2,51,52] that are both low voltage and low power.…”

Section: Introductionmentioning

confidence: 99%

Liquid-Metal-Based Reconfigurable Components for RF Front Ends

et al. 2015

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All Rights Reserved AcknowledgmentsI feel that this is a rare opportunity for me to share a bit of candidness and hope to make the most of it. I truly owe the completion of this thesis to many friends and family members and am sorry that I cannot thank you all. hope we can all stay in touch and get a bite and a drink together every once in a while. To leave off I would like to quote Andy Morishita and say "memories are made together" and I will always cherish these past few years we all had. This thesis focuses on the development of liquid-metal-based reconfigurable components for radio-frequency (RF) front ends. Reconfigurable components allow the RF front end to dynamically change key radio parameters such as output power, signal carrier frequency, and bandwidth. These capabilities enable the radio transceiver to adapt to environmental and communication channel changes on the fly, according to programmed protocols and priorities. As a low-loss metallic conductor, the liquid metal Galinstan is well suited for RF applications, and its fluidic nature makes it a natural candidate for reconfigurable architectures. Three liquid-metal based components are described: a frequency-tunable substrate integrated waveguide cavity filter, an electromagnetic bandgap phase shifter, and a frequency-reconfigurable slot antenna. These components are designed, fabricated, and tested and the advantages and disadvantages of using liquid metal are discussed. iv

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Giant and switchable surface activity of liquid metal via surface oxidation

Cited by 345 publications

References 42 publications

Field‐Controlled Electrical Switch with Liquid Metal

Field‐Controlled Electrical Switch with Liquid Metal

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Liquid-Metal-Based Reconfigurable Components for RF Front Ends

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