We report magnetic-field-driven on-demand manipulation of liquid metal in microfluidic channels filled with base or acid.

We report magnetic-field-induced liquid metal droplet on-demand manipulation by coating a liquid metal with ferromagnetic materials. The gallium-based liquid metal alloy has a challenging drawback that it is instantly oxidized in ambient air, resulting in surface wetting on most surfaces. When the oxidized surface of the droplet is coated with ferromagnetic materials, it is non-wettable and can be controlled by applying an external magnetic field. We coated the surface of a liquid metal droplet with either an electroplated CoNiMnP layer or an iron (Fe) particle by simply rolling the liquid metal droplet on an Fe particle bed. For a paper towel, the minimum required magnetic flux density to initiate movement of the ~8 μL Fe-particle-coated liquid metal droplet was 50 gauss. Magnetic-field-induced liquid metal droplet manipulation was investigated under both horizontal and vertical magnetic fields. Compared to the CoNiMnP-electroplated liquid metal droplet, the Fe-particle-coated droplet could be well controlled because Fe particles were uniformly coated on the surface of the droplet. With a maximum applied magnetic flux density of ~1,600 gauss, the CoNiMnP layer on the liquid metal broke down, resulting in fragmentation of three smaller droplets, and the Fe particle was detached from the liquid metal surface and was re-coated after the magnetic field had been removed.

We report a “magnetic liquid metal marble” (MLMM) obtained by coating a liquid metal’s surface with micro/nano-sized ferromagnetic iron (Fe) particles, which enables on-demand, magnetic manipulation of a liquid metal droplet for switching applications. Among liquid metals, gallium-based liquid metal alloys have been developed for a variety of applications. However, most developed applications using the gallium-based liquid metal alloy only work on deformability because of its easy-wetting property stemming from surface oxidation. By coating the oxidized surface with the 45 $\mu \text{m}$ or 45 nm diameter Fe particles, the MLMM exhibits non-wetting property investigated by evaluating apparent contact angles and sliding angles against various surfaces. On the Teflon-coated glass, the largest contact angle was measured to be ~169.0°, and the lowest sliding angle was obtained to be 17.2°, respectively. In order to move the 45- $\mu \text{m}$ diameter Fe particles-coated MLMM, we measured the minimum required magnetic flux density of 150 gauss and demonstrated the magnetic control of the liquid metal marble to turn ON light emitting diodes. In addition, we investigated that hydrochloric acid-vapor treatment on the MLMM enhanced the lyophobicity (sliding angle of 9.4°), reduced the minimum magnetic flux density (150 to 107 gauss) to actuate it, and enabled electrical switching applicability even in silicon oil with shorter delay time and high mobility of the MLMM under the applied magnetic field. [2015-0329]

In this paper, we report three-dimensional (3-D) liquid metal manipulation using electromagnets, which can be applied to electrical switching applications.

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.

We report magnetic field-driven dynamic morphological change of a liquid metal droplet: deformation and recovery; separation and merge. Low melting, non-toxic gallium-based liquid metal has been widely investigated due to its material properties and thus utilized to various applications. Morphological change of the liquid metal in required to tune characteristics of application. In order to enable the liquid metal to be non-wettable and magnetically controllable, we coated the surface with ferromagnetic iron (Fe) particles using hydrochloric acid (HCl) solution resulting in a magnetic liquid metal marble. With and without magnetic field, Fe particles-coated magnetic liquid metal marble was deformed and recovered readily. Against ~8 μL magnetic liquid metal marble, depending on the coated Fe particles mass, the shape deformation under magnetic field was changed: conventional (Fe < 4mg) and arbitrary (Fe ≥q 4mg) wetting shape. Accordingly, the deformability and recovery time of the magnetic liquid metal marble were varied. With an applied magnetic field, one marble was readily separated into 2, 3, and 4 marbles. Due to re-oxidation of the magnetic liquid metal marble surface, we treated the marble with HCl solution and vapor. Split and merge occurred depending on treatment time of HCl solution or vapor. Finally, we demonstrated magnetic field-based dynamic behavior which is reversible. [2020-0218]