Acoustic assembly of liquid metal particles into flexible electronics

Electronics with high stretchability and toughness are essential to designing soft robotics, skin electronics, and implantable medical devices. Gallium-based liquid metals (GaLM) – gallium alloys that are liquid at room temperature – are attractive for these devices as they generally have low toxicity and high thermal conductivities, in addition to their extreme deformity. However, fabricating stretchable conductive circuits using GaLM-polymer composites has remained challenging. Here, Wonbeom Lee and colleagues present a new approach that uses an acoustic field to assemble a network of liquid metal particles inside a polymer matrix. Because of their liquid state, complex GaLM circuits can be printed onto a surface as a string of liquid metal particles. However, when exposed to oxygen, these alloys tend to form an oxide skin. Although this can help GaLM microdroplets adhere to a polymer surface, it also insulates them from electrical conductivity. By exposing these droplets to an acoustic field, Lee et al. show that they shed off smaller nanodroplets that create a conductive bridge, or liquid metal particle network (LMP_Net), between the insulated microdroplets. When stretched, the authors show that the micro- and nanodroplets deform yet continue to maintain a highly conductive connection. What’s more, the authors demonstrate the approach’s universality by creating the acoustically generated LMP_Net in various polymer matrices, including hydrogels, a self-healing elastomer and photoresists, highlighting their potential for use in soft electronics. “The method presented by Lee et al. helps to overcome a major challenge in creating conductive circuits with GaLM-polymer composites, but the composites still face a number of manufacturing challenges,” write Ruirui Qiao and Shi-Yang Tang in a related Perspective.