Quantifying macro- and microscale alignment of carbon microfibers in polymer-matrix composite materials fabricated using ultrasound directed self-assembly and 3D-printing

Aligning microfibers along a user-specified direction is important to fabricate polymer-matrix composite materials with tailored properties, including anisotropic electrical and thermal conductivity and high strength-to-weight ratio. Building on our earlier work, we employ ultrasound directed self-assembly to align carbon microfibers along user-specified directions in photopolymer resin and use stereolithography to cure the resin and 3D print composite materials. We quantify macro- and microscale alignment of microfibers in the matrix as a function of weight fraction and dimensionless ultrasound transducer separation distance and input power. Multiple regression analysis expresses microfiber alignment as a function of the fabrication process parameters and shows that microscale alignment is primarily determined by microfiber weight fraction, whereas macroscale alignment is a function of microfiber weight fraction, dimensionless ultrasound transducer separation distance and input power. Relating microfiber alignment to the fabrication process parameters is a crucial step towards 3D-printing polymer-matrix composite materials with tailored material properties.