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Micromachines
Special Issues
Multifunctional Liquid Metal and Its Applications
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Multifunctional Liquid Metal and Its Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (28 April 2022) | Viewed by 17530

Special Issue Editors

Dr. Daeyoung Kim

E-Mail Website
Guest Editor
Deaprtment of Electrical Engineering, Korea Army Academy at Yeong-cheon, 495 Hogukro, Gogyeong-myeon, Yeongcheon-si 770-849, Gyeongbuk, Korea
Interests: MEMS; liquid metal microfluidics and applicatons; surface wettability
Prof. Dr. Jeong-Bong Lee

E-Mail Website
Guest Editor
Electrical and Computer Engineering, Baylor University, Waco, TX 76798-7356, USA
Interests: MEMS; liquid metals; nanophotonic; bio devices; sensors
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As the demand for developing flexible and wearable electronics is continuously increasing, deformable and electrical materials, such as liquid metal, have been in the spotlight. As an emerging material, the gallium-based liquid metal alloy has been extensively investigated because of its superior material properties. Unlike mercury, liquid metal is non-toxic and has outstanding features, such as a higher electrical and thermal conductivity, higher surface tension, higher boiling point, and lower vapor pressure. Based on these favorable properties, utilizing microfluidic technologies, liquid metals have been studied in order to be multifunctional in broad applications such as tunable antennas and metamaterials, switches and pumps, cooling devices, energy harvesters, sensors, and inkjet printing. Thus, in this Special Issue of Micromachines, we will explore multifunctional liquid metal properties and their various applications.

Prof. Dr. Daeyoung Kim
Prof. Dr. Jeong-Bong Lee
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Gallium-based liquid metal alloys
  • Microfluidics
  • Lab-on-a-chip
  • Flexible electronics
  • Wearble electronics
  • Soft electronics
  • Sensors
  • Applications

Published Papers (6 papers)

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Research

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8 pages, 1697 KiB  
Article
Design and Synthesis of Cobalt-Based Hollow Nanoparticles through the Liquid Metal Template
by Yuan Ji, Zhenlong Li, Yundan Liu, Xianghua Wu and Long Ren
Micromachines 2022, 13(8), 1292; https://doi.org/10.3390/mi13081292 - 11 Aug 2022
Cited by 1 | Viewed by 1410
Abstract
Co-based compounds have attracted much attention due to their competitive catalytic activities. To enhance their intrinsic electrocatalytic activity, morphology engineering is one of the effective strategies. Hollow structures have fascinating properties due to their low density and high loading capacity. In this work, [...] Read more.
Co-based compounds have attracted much attention due to their competitive catalytic activities. To enhance their intrinsic electrocatalytic activity, morphology engineering is one of the effective strategies. Hollow structures have fascinating properties due to their low density and high loading capacity. In this work, we introduce a Ga-based liquid alloy as a reactive template for the synthesis of varying Co-based hollow nanoparticles. The fluidity character of the Ga-based liquid alloy facilitates the large-scale production of nanoparticles via a top-down shearing process. The pre-installed active species (here is Zn) in the liquid alloy serve as a sacrificial source to quantitatively reduce Co2+ ions and form Co-based compounds. Well-structured Ga/CoOOH core-shell nanospheres are thus successfully prepared, and more varied Co-based hollow nanoparticles can be obtained by post-treatment and reaction. Hollow structures can offer enhanced interfacial area and increased active sites, benefiting the catalytic performance. Among the prepared Co-based catalysts, CoSe2 hollow nanoparticles exhibited the best oxygen evolution reaction (OER) activity with an overpotential of 340 mV at the current density of 10 mA/cm2. This work provides a novel strategy for the rational design and simple preparation of hollow nanoparticles. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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12 pages, 3021 KiB  
Article
Acoustic Wave-Driven Liquid Metal Expansion
by Youngbin Hyun, Jeong-Bong Lee, Sangkug Chung and Daeyoung Kim
Micromachines 2022, 13(5), 685; https://doi.org/10.3390/mi13050685 - 28 Apr 2022
Viewed by 1946
Abstract
In this paper, we report a volume expansion phenomenon of a liquid metal droplet naturally oxidized in an ambient environment by applying an acoustic wave. An oxidized gallium-based liquid metal droplet was placed on a paper towel, and a piezo-actuator was attached underneath [...] Read more.
In this paper, we report a volume expansion phenomenon of a liquid metal droplet naturally oxidized in an ambient environment by applying an acoustic wave. An oxidized gallium-based liquid metal droplet was placed on a paper towel, and a piezo-actuator was attached underneath it. When a liquid metal droplet was excited by acoustic wave, the volume of liquid metal was expanded due to the inflow of air throughout the oxide crack. The liquid metal without the oxide layer cannot be expanded with an applied acoustic wave. To confirm the effect of the expansion of the oxidized liquid metal droplet, we measured an expansion ratio, which was calculated by comparing the expanded size in the x (horizontal), y (vertical) axis to the initial size of the liquid metal droplet, using a high-speed camera. For various volumes of the droplet, when we applied various voltages in the range of 5~8 Vrms with 18.5~24.5 kHz using the piezo-actuator, we obtained a maximum expansion ratio of 2.4 in the x axis and 3.8 in the y axis, respectively. In addition, we investigated that the time to reach the maximum expansion in proportion to the volume size of liquid metal differed by five times from 4 s to 20 s, and that the time to maintain the maximum expansion differed from 23 s to 2.5 s, which was inversely proportional to the volume size. We also investigated the expansion ratios depending on the exposure time to the atmosphere. Finally, a circuit containing LED, which can be turned on by expanded liquid metal droplet, was demonstrated. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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11 pages, 37615 KiB  
Article
Sequential Oxidation Strategy for the Fabrication of Liquid Metal Electrothermal Thin Film with Desired Printing and Functional Property
by Jun-Heng Fu, Xu-Dong Zhang, Peng Qin and Jing Liu
Micromachines 2021, 12(12), 1539; https://doi.org/10.3390/mi12121539 - 10 Dec 2021
Cited by 3 | Viewed by 2104
Abstract
Room temperature liquid metal (LM) showcases a great promise in the fields of flexible functional thin film due to its favorable characteristics of flexibility, inherent conductivity, and printability. Current fabrication strategies of liquid metal film are substrate structure specific and sustain from unanticipated [...] Read more.
Room temperature liquid metal (LM) showcases a great promise in the fields of flexible functional thin film due to its favorable characteristics of flexibility, inherent conductivity, and printability. Current fabrication strategies of liquid metal film are substrate structure specific and sustain from unanticipated smearing effects. Herein, this paper reported a facile fabrication of liquid metal composite film via sequentially regulating oxidation to change the adhesion characteristics, targeting the ability of electrical connection and electrothermal conversion. The composite film was then made of the electrically resistive layer (oxidizing liquid metal) and the insulating Polyimide film (PI film) substrate, which has the advantages of electrical insulation and ultra-wide temperature working range, and its thickness is only 50 μm. The electrical resistance of composite film can maintain constant for 6 h and could work normally. Additionally, the heating film exhibited excellent thermal switching characteristics that can reach temperature equilibrium within 100 s, and recovery to ambient temperature within 50 s. The maximum working temperature of the as-prepared film is 115 °C, which is consistent with the result of the theoretical calculation, demonstrating a good electrothermal conversion capability. Finally, the heating application under extreme low temperature (−196 °C) was achieved. This conceptual study showed the promising value of the prototype strategy to the specific application areas such as the field of smart homes, flexible electronics, wearable thermal management, and high-performance heating systems. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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15 pages, 13445 KiB  
Article
Electric Field-Driven Liquid Metal Droplet Generation and Direction Manipulation
by Jinwon Jeong, Sangkug Chung, Jeong-Bong Lee and Daeyoung Kim
Micromachines 2021, 12(9), 1131; https://doi.org/10.3390/mi12091131 - 20 Sep 2021
Cited by 6 | Viewed by 3732
Abstract
A gallium-based liquid metal got high attention recently, due to the excellent material properties that are useful in various research areas. We report here on electric field-induced liquid metal droplet generation and falling direction manipulation. The well-analyzed electro-hydrodynamic method is a selectable way [...] Read more.
A gallium-based liquid metal got high attention recently, due to the excellent material properties that are useful in various research areas. We report here on electric field-induced liquid metal droplet generation and falling direction manipulation. The well-analyzed electro-hydrodynamic method is a selectable way to control the liquid metal, as the liquid metal is conductive. The electric field-induced liquid metal manipulation can be affected by the flow rate (0.05~0.2 mL/min), voltage (0~7 kV), and distance (15 and 30 mm) between electrodes, which changes the volume of the electric field-induced generated liquid metal droplet and the number of the generated droplets. When the electric field intensity increases or the flow rate increases, the generated droplet volume decreases, and the number of droplets increases. With the highest voltage of 7 kV with 15 mm between electrodes at the 0.2 mL/min flow rate, the lowest volume and the largest number of the generated droplets for 10 s were ~10 nL and 541, respectively. Additionally, we controlled the direction of the generated droplet by changing the electric field. The direction of the liquid metal droplet was controlled with the maximum angle of ~12°. Moreover, we exhibited a short circuit demonstration by controlling the volume or falling direction of the generated liquid metal droplet with an applied electric field. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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8 pages, 1959 KiB  
Article
Reconfigurable Metasurface Antenna Based on the Liquid Metal for Flexible Scattering Fields Manipulation
by Ting Qian
Micromachines 2021, 12(3), 243; https://doi.org/10.3390/mi12030243 - 28 Feb 2021
Cited by 10 | Viewed by 2903
Abstract
In this paper, we propose a reconfigurable metasurface antenna for flexible scattering field manipulation using liquid metal. Since the Eutectic gallium indium (EGaIn) liquid metal has a melting temperature around the general room temperature (about 30 °C), the structure based on the liquid [...] Read more.
In this paper, we propose a reconfigurable metasurface antenna for flexible scattering field manipulation using liquid metal. Since the Eutectic gallium indium (EGaIn) liquid metal has a melting temperature around the general room temperature (about 30 °C), the structure based on the liquid metal can be easily reconstructed under the temperature control. We have designed an element cavity structure to contain liquid metal for its flexible shape-reconstruction. By melting and rotating the element structure, the shape of liquid metal can be altered, resulting in the distinct reflective phase responses. By arranging different metal structure distribution, we show that the scattering fields generated by the surface have diverse versions including single-beam, dual-beam, and so on. The experimental results have good consistency with the simulation design, which demonstrated our works. The presented reconfigurable scheme may promote more interest in various antenna designs on 5G and intelligent applications. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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Review

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34 pages, 10241 KiB  
Review
Mini/Micro/Nano Scale Liquid Metal Motors
by Li Liu, Dawei Wang and Wei Rao
Micromachines 2021, 12(3), 280; https://doi.org/10.3390/mi12030280 - 08 Mar 2021
Cited by 15 | Viewed by 3464
Abstract
Swimming motors navigating in complex fluidic environments have received tremendous attention over the last decade. In particular, liquid metal (LM) as a new emerging material has shown considerable potential in furthering the development of swimming motors, due to their unique features such as [...] Read more.
Swimming motors navigating in complex fluidic environments have received tremendous attention over the last decade. In particular, liquid metal (LM) as a new emerging material has shown considerable potential in furthering the development of swimming motors, due to their unique features such as fluidity, softness, reconfigurability, stimuli responsiveness, and good biocompatibility. LM motors can not only achieve directional motion but also deformation due to their liquid nature, thus providing new and unique capabilities to the field of swimming motors. This review aims to provide an overview of the recent advances of LM motors and compare the difference in LM macro and micromotors from fabrication, propulsion, and application. Here, LM motors below 1 cm, named mini/micro/nano scale liquid metal motors (MLMTs) will be discussed. This work will present physicochemical characteristics of LMs and summarize the state-of-the-art progress in MLMTs. Finally, future outlooks including both opportunities and challenges of mini/micro/nano scale liquid metal motors are also provided. Full article
(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)
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