Magnetic liquid metal marble: Wireless manipulation of liquid metal droplet for electrical switching applications

We report a magnetic liquid metal marble which enables the wireless on-demand manipulation of a liquid metal droplet for electrical switching applications with an applied magnetic field. Gallium-based liquid metal alloy has been applied to various applications but most applications are based on deformability due to its surface wettability originating from the natural oxide layer. We suggested and demonstrated a `magnetic liquid metal marble´ by coating the oxidized surface of the liquid metal with ferromagnetic iron (Fe) particles. It shows non-wetting characteristics by measuring static and sliding contact angles against different surfaces such as a glass slide, a Teflon-coated glass, and polydimethylsiloxane (PDMS). On the Teflon-coated glass, the largest contact angle of 169.0 ± 1.3° was achieved for 45 nm diameter Fe particles-coated magnetic liquid metal marble, and the lowest sliding angle of 17.2° was achieved for 45 μm diameter Fe particles coated-magnetic liquid metal marble, respectively. We also studied the minimum required magnetic field of 150 gauss to mobilize the 45 μm diameter Fe particles coated-magnetic liquid metal marble and demonstrated the on-demand wireless magnetic manipulation of the liquid metal marble to power light emitting diodes (LEDs).