their range of applications could be substantially extended beyond the traditional ones based on liquid metals as a continuous fluid. To date, liquid-metal particles of micro-or nano-sizes have demonstrated promising performances in diverse research areas such as self-healing electronics, [8,9] thermal interface materials, [10,11] catalytic reaction implementation, [12] drug delivery, [13] and plasmonics. [14] Among the various methods developed for manufacturing liquid-metal particles, [15,16] sonication is most commonly employed, [5][6][7] which breaks the bulk liquid metal into small entities in a desired solvent. The dispersed liquid-metal particles have a thin oxide skin that forms spontaneously on a surface, [1] which prevents liquidmetal droplet coalescence and allows them to maintain their particulate form. The modulation of the surface oxide, typically with the support of surface-bound ligands, [17,18] can be used to precisely control the mechanical, electrical, and optical properties of liquid-metal particles that carry the liquid-state core under the outermost oxide surface. This can provide unique opportunities that are inaccessible by conventional all-solid-state metal and metal oxide particles.Despite the large number of studies on the preparation and applications of micro-and nano-sized liquid-metal particles reported to date, less attention has been focused on the colloidal behavior of such particles suspended in liquid media. To the best of our knowledge, no studies have been conducted on liquid-metal colloids in highly nonpolar organic solvents such as saturated hydrocarbons. Nonpolar colloidal dispersions are crucial in various industrial applications, the best-known example of which is the electronic ink embedded in an electrophoretic display. [19][20][21][22] Owing to the low electrical conductivity of nonpolar solvents, the power consumption of electrophoretic displays is low, which can be beneficial in the development of emerging portable and wearable Internet-of-Things (IoT) devices. Thus, classical electronic ink technology was recently combined with a triboelectric nanogenerator (TENG) to develop self-powered and low-power-consumption electronic paper. [23] Other useful applications of nonpolar dispersions include oilbased printing toners for electrostatic lithographic printers, [24] electrorheological fluids, [25,26] photonic crystals, [27] and drug delivery systems. [28] While conventional nonpolar dispersions used in such applications employ all-solid-state particles, new Liquid metals and alloys are attracting renewed attention owing to their potential for application in various advanced technologies. Eutectic galliumindium (EGaIn) has been focused on in particular because of its integrated advantages of high conductivity, low melting point, and low toxicity. In this study, the colloidal behavior of nano-dispersed EGaIn in nonpolar oils is investigated. Although the nonpolar oil continuous phase is commonly considered to be free of electric charges, electrostatic repulsion appears to...

This paper presents a technology for the removal of bubbles using the two mechanisms of electric and acoustic actuation. In this study, dielectrowetting was used to separate bubbles from the surface of a substrate, while acoustic actuation was used to transfer and eliminate separated bubbles by acoustically exciting them. In addition, the electrical signals of various voltages and frequencies were applied to patterned electrodes fabricated through the standard microfabrication processes in order to investigate the dynamic behaviors of the dielectrowetting driven bubbles, such as the contact angles of the bubbles and their separated distances from the surface. Furthermore, a high-speed camera was used to measure the velocities of single bubbles separated from the surface through acoustic excitation at various frequencies in order to identify the velocity and efficiency at which bubbles were transported and removed by acoustic excitation. To test the feasibility of removing multiple bubbles of various volumes, an experiment was carried out in which the proposed dielectrowetting and acoustic actuation were used to separate bubbles of different volumes from the surface simultaneously and then remove them. The experiment revealed that multiple bubbles of various volumes could be removed all at once in a second. The proposed method of removing bubbles can be used in a variety of industrial applications that require the transfer of large quantities of heat.

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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.