Combining ultrasound directed self-assembly and stereolithography to fabricate engineered polymer matrix composite materials with anisotropic electrical conductivity

Engineered polymer matrix composite materials with designer electrical properties are important for a myriad of engineering applications including flexible electronics, electromagnetic shielding, and materials with embedded electrical wiring. However, existing fabrication methods are limited by material choice and dimensional scalability. We use the acoustic radiation force associated with a standing ultrasound wave field to spatially arrange and align electrically conductive microfibers dispersed in a photopolymer matrix in user-specified orientations and use stereolithography to solidify the material. We relate the electrical conductivity of the material specimens to the fabrication process parameters, including ultrasound transducer power, microfiber alignment, and microfiber weight fraction. Logistic regression analysis demonstrates that the probability that a composite material specimen is electrically conductive increases with increasing microfiber weight fraction and microfiber alignment because these parameters drive the formation of a long-range percolated network of electrically conductive microfibers. We determine that the electrical conductivity of conductive specimens ranges between 31 - 793 S/m and that the fabrication process parameters are critical in predicting whether a composite material specimen is electrically conductive or insulating. Relating the composite material fabrication process parameters to the resulting electrical conductivity is a crucial step towards fabricating polymer matrix composite materials with designer electrical properties for use in engineering applications. The combined ultrasound DSA and SLA fabrication process works independent of fiber and matrix material properties and facilitates dimensional scalability due to low attenuation of ultrasound waves in viscous media.

Automated summary

The spatial arrangement and alignment of electrically conductive microfibers in a polymer matrix using acoustic radiation force and ultrasound technology are key factors in determining the electrical properties of composite materials. The probability of a material specimen being electrically conductive is influenced by parameters such as microfiber weight fraction and alignment, which contribute to the formation of a long-range percolated network of conductive microfibers. The combination of ultrasound DSA and SLA fabrication process is independent of fiber and matrix material properties, enabling dimensional scalability for engineering applications.