Flexible Composites with Programmed Electrical Anisotropy Using Acoustophoresis

A single-step process that utilizes acoustophoresis to modulate the electrical properties of composites is developed to address the demand for 3-D printing multifunctional materials. Here, acoustic fields assemble conductive particles into networks within polymer matrices, whose configuration is modulated prior to curing to produce 2-D conductive, 1-D conductive, or insulating materials on-demand, all using the same precursor ink. These variously patterned materials, used as electrical interconnects, are demonstrated to yield discrete, useful outputs from an electrical circuit. Furthermore, patterning efficient percolated networks in this way increases conductivity an order of magnitude over conventional dispersed-fiber composites, which rely on inefficient stochastic networks, to >5000 S/m bulk conductivity (2.6v% silver-coated fibers; 97% network efficiency). Similarly, these efficient networks require an order of magnitude lower particle loading than dispersed-fiber composites, improving printability and allowing versatile orthogonal control of other properties. As a demonstration of this multifunctional control, conductive elastomeric composites made with this method are demonstrated to withstand >500 bending cycles to a radius of 0.7 mm without losses in conductivity. This technology demonstrates a novel approach to modulating material properties via on-the-fly microstructure control to pave the way for 3D printing components with embedded electrical circuits or other spatially modulated properties.