Liquid-Metal-Coated Magnetic Particles toward Writable, Nonwettable, Stretchable Circuit Boards, and Directly Assembled Liquid Metal-Elastomer Conductors.

Liquid metal is a promising conductor material for producing soft and stretchable circuit "boards" that can enable next-generation electronics by electrically connecting and mechanically supporting electronic components. While liquid metal in general can be used to fabricate soft and stretchable circuits, magnetic liquid metal is appealing because it can be used for self-healing electronics and actuators by external magnetic fields. Liquid metal can be rendered into particles that can then be used for sensors and catalysts through sonication. We used this feature to produce "novel" conductive and magnetic particles. Mixing ferromagnetic iron particles into the liquid metal (gallium) produces conductive ferrofluids that can be rendered into gallium-coated iron particles by sonication. The gallium shell of the particles is extremely soft, while the rigid iron core can induce high friction in response to mechanical pressure; thus, hand-sintering of the particles can be used to directly write the conductive traces when the particles are cast as a film on elastic substrates. The surface topography of the particles can be manipulated by forming GaOOH crystals through sonication in DI water, thus resulting in nonwettable circuit boards. These gallium-coated iron particles dispersed in uncured elastomer can be assembled to form conductive microwires with the application of magnetic fields.