Factors Influencing the Orientation of Carbon Nanotubes in Flexible and Lightweight Composite Ribbons during Direct Ink Writing.

Direct ink writing (DIW) is an automated, fast, and large-scale fabrication technique that combines controlled ink extrusion in predesigned patterns on various rigid or flexible substrates. In this study, we present a detailed investigation of the key factors that influence the carbon nanotube (CNT) orientation in line patterns created through DIW and in ribbons obtained from their removal. We have comprehensively examined how the composition and dispersion quality of CNT/polymer composite ink, substrate wettability, and various drawing parameters affect the CNT orientation. The optimal degree of orientation, measured by the Raman scattering intensity ratio between parallel and perpendicular directions, reached a value of 3.72, leading to a 3.8-fold improvement in thermal conductivity (109 W/mK) and a 57.7-fold enhancement in electrical conductivity (1733 S/cm) compared with the isotropic control samples. A theoretical model was developed to analyze CNT alignment through shear stress in the needle by incorporating the relationship between the ink viscosity and drawing parameters. The insights gained from this study will not only aid in controlling the CNT orientation but can also be applied to other quasi-dimensional nanomaterials.