On-Demand Programming of Liquid Metal-Composite Properties Through Direct Ink Write 3D Printing

Soft, elastically deformable composites with liquid metal (LM) droplets can enable new generations of soft electronics, robotics, and reconfigurable structures. However, techniques to control local composite microstructure, which ultimately governs material properties and performance, is lacking. Here, a direct ink writing technique is developed to program the LM microstructure (i.e., shape, orientation, and connectivity) on-demand throughout elastomer composites. This technique enables the creation of filaments, films, and 3D structures with unique LM microstructures that are generated on-demand and locked in during printing. By tuning ink rheology, the microstructure of LM droplets can be controlled in a wide range of ink materials. Through this control of microstructure, we show the ability to systematically tune mechanical and functional properties throughout a printed part with a single ink and a single nozzle. This is highlighted with anisotropic thermal conductivity, enhanced electrical conductivity, and unique mechanical properties such as tunable modulus and toughness due to the microstructure of LM inclusions. This methodology for programming properties in soft multifunctional materials combines material composition and process parameters, leading to greatly enhanced performance for emerging technologies that demand mechanical compliance with multifunctional response.