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Emerging applications of liquid metals featuring surface oxides.

Dickey MD - ACS Appl Mater Interfaces (2014)

Bottom Line: Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface.The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance.Here, we show that this solid oxide "skin" enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, North Carolina State University , Raleigh, North Carolina 27695, United States.

ABSTRACT
Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide "skin" enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

No MeSH data available.


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Crossbar array memory device (i.e., memristor)composed of hydrogel and liquid metal. (a) Photograph of a prototypeof an integrated soft memristor circuit with a 2 × 2 crossbararray. The device is flexible as shown in the inset image and compatiblewith water. (b) Schematic of the prototype in a. The arrows pointto the nodes, consisting of two different hydrogels sandwiched betweenliquid metal electrodes. (c) Switching bias to turn “off”(+ 5 V) and “on” (−5 V) the nodes is appliedto the 1-B node for the first and second cycles and to the 2-A nodefor the third cycle, respectively, as shown by the arrows. The filledsymbols represent the nodes in the “off” state. Adaptedwith permission from ref (99). Copyright 2011 Wiley.
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fig10: Crossbar array memory device (i.e., memristor)composed of hydrogel and liquid metal. (a) Photograph of a prototypeof an integrated soft memristor circuit with a 2 × 2 crossbararray. The device is flexible as shown in the inset image and compatiblewith water. (b) Schematic of the prototype in a. The arrows pointto the nodes, consisting of two different hydrogels sandwiched betweenliquid metal electrodes. (c) Switching bias to turn “off”(+ 5 V) and “on” (−5 V) the nodes is appliedto the 1-B node for the first and second cycles and to the 2-A nodefor the third cycle, respectively, as shown by the arrows. The filledsymbols represent the nodes in the “off” state. Adaptedwith permission from ref (99). Copyright 2011 Wiley.

Mentions: In the previous examples,the metal is simply serving as a conductive element. The metal can,however, be utilized in a more active way to create soft electronicdevices. Combining the metal with hydrogel allows for the creationof memristor (memory-resistor) devices99 and diodes100 composed almost entirelyfrom liquids, since hydrogels are largely composed of water. Figure 10 shows photographs of these devices. These softdevices have the appeal of being matched mechanically to biologicalsystems, built largely from biocompatible materials (hydrogels), operatein an aqueous and ionic environment, and in the case of the memristors,use hysteretic memory; the brain also uses hysteretic memory and memristorsare proposed to replicate their behavior. The details behind the operationof these devices are complicated, but may be understood simply asemploying interfacial electrochemistry to control the thickness ofthe oxide. Contacting the hydrogel to the liquid metal allows forelectrochemical reactions to occur at the interface. Oxidative biascauses the oxide to thicken (i.e., anodization) and thus become moreresistive. Reductive bias causes the oxide to thin and thus becomemore conductive (between the metal and the gel). Figure 9c shows the changes in conductivity of individual junctionsof the device depicted in Figure 9a, b. Thememristor assigns the resistive and conductive states as the 1 and0 necessary for digital memory. The diode works under a similar principlein which the current between the liquid metal and the gel dependson the polarity of the electrode.


Emerging applications of liquid metals featuring surface oxides.

Dickey MD - ACS Appl Mater Interfaces (2014)

Crossbar array memory device (i.e., memristor)composed of hydrogel and liquid metal. (a) Photograph of a prototypeof an integrated soft memristor circuit with a 2 × 2 crossbararray. The device is flexible as shown in the inset image and compatiblewith water. (b) Schematic of the prototype in a. The arrows pointto the nodes, consisting of two different hydrogels sandwiched betweenliquid metal electrodes. (c) Switching bias to turn “off”(+ 5 V) and “on” (−5 V) the nodes is appliedto the 1-B node for the first and second cycles and to the 2-A nodefor the third cycle, respectively, as shown by the arrows. The filledsymbols represent the nodes in the “off” state. Adaptedwith permission from ref (99). Copyright 2011 Wiley.
© Copyright Policy - editor-choice
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4231928&req=5

fig10: Crossbar array memory device (i.e., memristor)composed of hydrogel and liquid metal. (a) Photograph of a prototypeof an integrated soft memristor circuit with a 2 × 2 crossbararray. The device is flexible as shown in the inset image and compatiblewith water. (b) Schematic of the prototype in a. The arrows pointto the nodes, consisting of two different hydrogels sandwiched betweenliquid metal electrodes. (c) Switching bias to turn “off”(+ 5 V) and “on” (−5 V) the nodes is appliedto the 1-B node for the first and second cycles and to the 2-A nodefor the third cycle, respectively, as shown by the arrows. The filledsymbols represent the nodes in the “off” state. Adaptedwith permission from ref (99). Copyright 2011 Wiley.
Mentions: In the previous examples,the metal is simply serving as a conductive element. The metal can,however, be utilized in a more active way to create soft electronicdevices. Combining the metal with hydrogel allows for the creationof memristor (memory-resistor) devices99 and diodes100 composed almost entirelyfrom liquids, since hydrogels are largely composed of water. Figure 10 shows photographs of these devices. These softdevices have the appeal of being matched mechanically to biologicalsystems, built largely from biocompatible materials (hydrogels), operatein an aqueous and ionic environment, and in the case of the memristors,use hysteretic memory; the brain also uses hysteretic memory and memristorsare proposed to replicate their behavior. The details behind the operationof these devices are complicated, but may be understood simply asemploying interfacial electrochemistry to control the thickness ofthe oxide. Contacting the hydrogel to the liquid metal allows forelectrochemical reactions to occur at the interface. Oxidative biascauses the oxide to thicken (i.e., anodization) and thus become moreresistive. Reductive bias causes the oxide to thin and thus becomemore conductive (between the metal and the gel). Figure 9c shows the changes in conductivity of individual junctionsof the device depicted in Figure 9a, b. Thememristor assigns the resistive and conductive states as the 1 and0 necessary for digital memory. The diode works under a similar principlein which the current between the liquid metal and the gel dependson the polarity of the electrode.

Bottom Line: Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface.The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance.Here, we show that this solid oxide "skin" enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, North Carolina State University , Raleigh, North Carolina 27695, United States.

ABSTRACT
Gallium and several of its alloys are liquid metals at or near room temperature. Gallium has low toxicity, essentially no vapor pressure, and a low viscosity. Despite these desirable properties, applications calling for liquid metal often use toxic mercury because gallium forms a thin oxide layer on its surface. The oxide interferes with electrochemical measurements, alters the physicochemical properties of the surface, and changes the fluid dynamic behavior of the metal in a way that has, until recently, been considered a nuisance. Here, we show that this solid oxide "skin" enables many new applications for liquid metals including soft electrodes and sensors, functional microcomponents for microfluidic devices, self-healing circuits, shape-reconfigurable conductors, and stretchable antennas, wires, and interconnects.

No MeSH data available.


Related in: MedlinePlus