A highly stretchable and sintering-free liquid metal composite conductor enabled by ferrofluid

Stretchable and highly conductive elastomers with intrinsically deformable liquid metal (LM) fillers exhibit promising potential in soft electronics, wearables, human-machine interfaces, and soft robotics. However, conventional LM-elastomer (LME) conductors require a high loading ratio of LM and the post-sintering to rupture LM particles to achieve electric conductivity, which results in high LM consumption and process complexity. In this work, we presented a straightforward and post-sintering-free method that utilizes magnetic aggregation to fabricate stretchable LME conductors. This was achieved by dispersing LM ferrofluid into the elastomer precursor, followed by applying the magnetic field to induce the aggregation and interconnection of the LM ferrofluid particles to form conductive pathways. This method not only simplifies the preparation of initially conductive LME but also reduces the LM loading ratio. The resulting conductive LME composites show high stretchability (up to 650% strain), high conductance stability, and magnetic responsiveness. The stretchable LME conductors were demonstrated in various applications, including the creation of flexible microcircuits, a magnetically controlled soft switch, and a soft hydrogel actuator for grasping tasks. We believe the stretchable LME conductors may find wide applications in electronic skins, soft sensors, and soft machines.