Acoustic patterning of 3D printed composites for anisotropic conductivity and multifunctionality

A versatile class of composite materials composed of functional filler particles in polymer matrices are increasingly used in high-performance applications that leverage their adaptable mechanical, electrical, thermal, and other functional properties. The choice of constituent materials largely determines these properties: for example, long fibers redistribute stress efficiently, highly conductive filler particles impart their conductivity to the material, and combinations of ionic and electrically conductive fillers with energy storage materials increase the capacity of battery electrodes. The performance of these composites, however, is highly dependent on the internal arrangement of particles. Consequently, controlling this internal structure enables property improvements and novel functionalities. In particular, combining microstructure control with the design freedom of 3D printing presents opportunities to maximize the performance of functional components by spatially modulating properties and their directionality (e.g. reinforcing high-stress regions, prescribing electrical interconnects, or directing heat away from hot spots), as well as introducing novel combinations of properties.To develop this structural control in printed materials, this work utilizes pressure fields to assemble filler particles into patterns within composites during 3D printing. Particle patterns are engineered to improve material properties by leveraging microscopic acoustic forces on particles, tailoring the particle arrangement for improvements in the functionality of the material. This acoustic patterning technique is integrated into 3D printing with attention to processing constraints (e.g. component and feature sizes, material properties, cost, throughput rate, etc.) required in existing and emerging technological applications. In particular, 3D printed composites with high electrical or thermal conductivity, which are simultaneously mechanically flexible or strain-tolerant, are