Adv Mater. 2022 Mar 30. e2200182
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 we develop a direct ink writing technique to program LM microstructure (i.e., shape, orientation, and connectivity) on demand throughout elastomer composites. In contrast to inks with rigid particles that have fixed shape and size, we show that emulsion inks with LM fillers enable in-situ control of microstructure. This enables filaments, films, and 3D structures with unique LM microstructures that are generated on demand and locked in during printing. This includes smooth and discrete transitions from spherical to needle-like droplets, curvilinear microstructures, geometrically complex embedded inclusion patterns, and connected LM pathways. The printed materials are soft (modulus < 200 kPa), highly deformable (> 600% strain), and can be made locally insulating or electrically conductive using a single ink by controlling process conditions. We demonstrate these capabilities by embedding elongated LM droplets in a soft heat sink, which rapidly dissipates heat from high power LEDs. These programmable microstructures can enable new composite paradigms for emerging technologies that demand mechanical compliance with multifunctional response. This article is protected by copyright. All rights reserved.
Keywords: 3D printing; additive manufacturing; liquid metal; microstructure; soft robots