Flexible Conductive Composites with Programmed Electrical Anisotropy Using Acoustophoresis

Developing mechanically flexible composite materials with high electrical conductivity is currently hindered by the need to use high loading of conductive filler, which severely limits flexibility. Here, acoustic focusing is used to control arrangement of conductive particles in photopolymer matrices to create composites with both tunable conductivity and flexibility. Acoustophoresis patterns filler particles into highly efficient percolated networks which utilize up to 97% of the particles in the composite, whereas the inefficient stochastic networks of conventional dispersed‐fiber composites utilize 500 bending cycles without losses in conductivity and changing conductivity only 5% within cycles on average. In contrast, conventional unpatterned composites with the same conductivity require such high loading that they are prohibitively brittle. Finally, modulating the applied acoustic field controls the anisotropy of the conductive networks and produces materials which are either 2D conductive, 1D conductive, or insulating, using the same nozzle and ink, paving the way for versatile multifunctional 3D printing. Mechanically flexible composite materials with high electrical conductivity are fabricated using acoustic focusing. This directed assembly technique arranges filler particles into efficient conductive structures, increasing conductivity while only requiring low particle volume fractions. Additionally, tuning acoustic assembly parameters controls transport anisotropy in the assembled networks, allowing modulation between isotropic conductive, anisotropic conductive, and insulating material using the same ink.