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 Perspectives.

- This press release was provided by American Association for the Advancement of Science