Hydrochloric acid-impregnated paper for gallium-based liquid metal microfluidics

Kim, Dae-Young; Lee, Yunho; Lee, Dong Weon; Choi, Wonjae; Yoo, Koangki; Lee, Jeong

doi:10.1016/j.snb.2014.09.108

Cited by 34 publications

(23 citation statements)

References 24 publications

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“…Using the reverse stamping process, molded EGaIn in predefined PDMS microchannels enables high‐resolution, residue‐free, and uniform lines. On the other hand, the physical surface modification creates a paper‐textured PDMS surface, increasing the surface areas and adhesion forces, ultimately enhancing wettability to form uniform and smooth EGaIn thin films using the additive stamping process.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, stamp lithography is often regarded as the lowest resolution and least reliable technique among the additive printing methods . By utilizing chemical and physical surface modification of the elastomeric substrates, the PDMS surfaces can be modified to have selective nonwetting or wetting properties for EGaIn: the nonwetting characteristics of chemically modified PDMS surfaces hinder formation of EGaIn residue, while the uniform wetting characteristics of physically modified PDMS surfaces assist to form thin and smooth EGaIn films. In combination, these wetting/nonwetting properties enable multiscale and uniform EGaIn thin‐film patterning in simple and effective manners.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Kim

Alrowais

et al. 2018

Adv Materials Technologies

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to healthcare. [5,6] Unlike conventional solid-state electronics, soft electronics can be lightweight, stretchable, and reconfigurable, with biocompatible characteristics for skin-mountable and wearable sensing electronics. [7,8] Thereby, flexible and stretchable characteristics are achieved by using either 2D or 3D compliant wave-like, solid metal patterns [9,10] or elastic conductors based on conductive nanomaterials embedded in a polymer matrix. [11,12] An alternative approach to realize all-soft microsystems is the use of intrinsically soft conductors, such as gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn). EGaIn-based soft electronics benefits from its nontoxicity, mechanical stability (unlimited stretchability, but ultimately limited by the mechanical properties of the encasing material), thermal conductivity (κ = 26.6 W m −1 K −1 ), and electrical conductivity (σ = 3.4 × 10 6 S m −1 ). [13][14][15] The low melting temperature (M P < 15 °C) and negligible vapor pressure of EGaIn facilitate room-temperature and ambient pressure manufacturing processing. [13][14][15] Moreover, thanks to the formation of a thin oxide layer (t ≈ 1-3 nm) on the EGaIn surface under atmospheric oxygen level, EGaIn structures maintain their mechanical shapes, [16,17] allowing 2D/3D EGaIn patterns on a soft elastomeric substrate, such as poly(dimethylsiloxane) (PDMS).The moldable characteristic of EGaIn has enabled a broad range of patterning methods based on lithography-enabled stamping and stencil printing, injection, as well as additive and subtractive direct write/patterning processes, [18][19][20] as summarized in Table S1 in the Supporting Information. Thereby, printing using lithography-defined stencils [21][22][23][24] yields simple and high throughput EGaIn patterning on elastomeric substrates with small features of w (width) ≈200 µm/t (thickness) ≈50 µm using metal stencil films, [21] w ≈ 20 µm/t ≈ 2 µm using microfabricated metal stencil films, [22] and w ≈ 20 µm/t ≈ 10 µm using polymer stencil films. [23] Limitations of this approach are the relatively low resolution, rough EGaIn surface, and excessive EGaIn loss during the stencil lift-off process. SubtractiveThe use of intrinsically soft conductors, such as gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn), has enabled bioinspired and skin-like soft electronics. Thereby, creating patterned, smooth, and uniform EGaIn thin films with high resolution and size scalability is one of the primary technical hurdles. Soft lithography using wetting/nonwetting surface modifications and 3D heterogeneous integration can address current EGaIn patterning challenges. This paper demonstrates multiscale and uniform EGaIn thin-film patterning by utilizing an additive stamping process for large-scale (mm-cm) soft electronics and a subtractive reverse stamping process for microscale (µm-mm) soft electronics. While EGaIn patterning based on stamping is regarded as the least reliable patterning technique, this paper highlights multiscale and uniform thin-fi...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Kim

Alrowais

et al. 2018

Adv Materials Technologies

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“…Both of these etchants mix readily with water and can be contained safely at high concentrations. A non‐aqueous alternative for oxide removal comes through exposing the liquid metals to concentrated HCl vapor, but practical applications of this are generally limited to environments that can withstand the presence of a highly corrosive gas.…”

Section: Contact Angles Of Galinstan Droplets On Various Substrates mentioning

confidence: 99%

Liquid Metal Switches for Environmentally Responsive Electronics

Bilodeau

Zemlyanov

Kramer

2017

Adv Materials Inter

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providing a second system for non-mechanical liquid metal manipulation. Zhang et al. fed aluminum chips to a galinstan droplet as fuel for self-propulsion, [19] and have since developed non-contacting magnetic controls for the droplet. [20] Finally, a large category of recent research has used electricity to create relative motion and shape change in liquid metals, [21][22][23] enabling non-contacting pumps for microfluidic flow [24] and cooling, [25] self-destructive circuitry (path-destructive liquid metal droplet motion), [26] and most recently as a source for rigid-body locomotion. [27] It is well known that gallium oxidizes rapidly in normal atmospheric conditions, or in any environment with oxygen levels above 1 ppm, [11,28,29] forming a gallium oxide that has been studied in detail. [30][31][32] This oxide is solid at room temperature and forms a nanoscale stabilizing shell around liquid gallium indium alloys, enabling the liquid metal to be patterned onto, and subsequently adhere to, many different material surfaces (via a plethora of techniques). [33] If the oxide is removed, the liquid metal loses its adhesion to the substrate and will reflow under the influence of gravity (or other forces), enabling a fixed liquid metal pattern to change. In other words, oxide removal enables real-time, non-mechanical manipulation of liquid metals. This has typically been done either in nitrogen boxes (via passive oxide prevention) or in chemical etchant baths (via active oxide removal). [18,19,21,[24][25][26] Unfortunately, these methods require enclosed (air-tight or water-proof) chambers that limit the practical applications for manipulation of liquid metal circuits on the fly, as the circuits must remain inside the chamber.The two main etchants used for aqueous oxide removal are hydrochloric acid (HCl, a low-pH acid) [15,18,21,30,31,34] and sodium hydroxide (NaOH, a high-pH base). [19,21,22,[24][25][26] Both of these etchants mix readily with water and can be contained safely at high concentrations. A non-aqueous alternative for oxide removal comes through exposing the liquid metals to concentrated HCl vapor, [35][36][37][38][39] but practical applications of this are generally limited to environments that can withstand the presence of a highly corrosive gas.In this work, we demonstrate control over the surface oxide of liquid metal droplets, which in turn controls the wetting and adhesion of those drops on a substrate, using purely environmental stimuli. We compare the use of highly acidic HCl and highly alkaline NaOH (in solution) in removing the oxide to release pinned droplets. We show that although both solvent solutions result in high contact angles between the droplet and the substrate, NaOH achieves this result at a rate that is orders of magnitude faster than HCl. We further explore the use of neutral distilled water to regrow the oxide and manipulate the contact area of the liquid metal droplet on the surface, causing the droplet to readhere to the substrate. Finally, we apply this environmentally control...

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“…The oxide skin prevents the complete removal of GaLMAs from microfluidic channels and surfaces because it strongly adheres to most surfaces and does not allow the high surface tension of the liquid to keep the fluid intact. The most prolific solution to this issue has been the use of highly concentrated acidic or basic solutions to chemically react with the surface to destabilize the mechanical rigidity of the oxide, which then allows the intrinsic high surface tension of the GaLMA to dictate its fluidic behavior . This approach has been effectively implemented in literature through various device architectures to enable reconfiguration of GaLMA fluids within microfluidic devices.…”

Section: Introductionmentioning

confidence: 99%

Ion Exchange Membranes as an Interfacial Medium to Facilitate Gallium Liquid Metal Alloy Mobility

Ilyas

Butcher

Durstock

et al. 2016

Adv Materials Inter

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Liquid metal electronics represent a groundbreaking advancement in electronic reconfigurability. Replacing mercury with nontoxic gallium liquid metal alloys (GaLMAs) will provide a significant improvement toward this paradigm; however, the metallic residues left behind on surfaces that contact GaLMAs have prevented their broad application to date. This report describes a novel method to control the wetting characteristics of GaLMAs by utilizing an ion exchange membrane (IEM) as an interface material that gradually releases minute concentrations of HCl vapor which reacts with the GaLMA surface and thus prevents residue formation. A common IEM, Nafion, is shown to behave both as an effective HCl transport medium and as a source for HCl vapor, and the chemical and phenomenological interactions of Nafion and HCl with GaLMA fluids are characterized. Additionally, an application of Nafion toward GaLMA microfluidics is demonstrated by integrating commercially available extruded Nafion tubes and by utilizing a solution suspension of Nafion to coat an arbitrary silicone‐based microfluidic matrix material. Both methods proved effective in generating a reversible flow system that remained residue free for extended periods of time, which can be regenerated without the use of concentrated acidic solutions.

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Hydrochloric acid-impregnated paper for gallium-based liquid metal microfluidics

Cited by 34 publications

References 24 publications

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Liquid Metal Switches for Environmentally Responsive Electronics

Ion Exchange Membranes as an Interfacial Medium to Facilitate Gallium Liquid Metal Alloy Mobility

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