Harnessing Anisotropic Particles in 3D Printable Silicone Inks

Anisotropic materials exhibit directionally dependent properties afforded by their microstructure and composition, enabling optimized performance. In this study, the incorporation of anisotropic particles within silicone inks that are 3D printable via direct ink writing (DIW) is harnessed to design materials with directionally dependent toughness and electrical conductivity. We describe the formation of anisotropic silicone particles through dispersion in aqueous media, where their shape and size can be adjusted by modifying the processing conditions and composition of each phase. Depending on the rheological properties of the aqueous medium and uncured silicone, particles can range from spherical to ellipsoidal to amorphous. These particles are subsequently cured, isolated, and incorporated as additives into custom DIW ink formulations. During printing, these anisotropic particles function as thixotropic additives to help maintain 3D shape and align in the direction of flow, resulting in anisotropic mechanical properties in the direction of printing. The particles were then formulated with electrically conductive fillers to introduce added functionality into the printed materials. Parallel plate rheology, microscopy, mechanical testing and electrical conductivity testing were used to evaluate the flow behavior, microstructure, and solid-state properties of the uncured inks and 3D printed structures. This work offers a versatile technique for tailoring the mechanical properties of silicone-based composites and provides a novel strategy for reducing the electrical percolation threshold, potentially advancing applications in flexible electronics and smart materials.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.