Carbon nanotubes have the ability to strongly bundle together via Van Der Waals forces to form lightweight macro materials with high electrical, mechanical, and thermal properties. Consequently, there has been a great interest in developing wet spun CNT fibers, since their promising properties can be used in a wide variety of applications such as cabling, wearable electronics, biomedical applications, and energy applications. CNT fiber technology has improved dramatically over time. However, the spinning process needs to become more efficient to decrease the CNT fiber's cost and environmental impact. The macroscopic properties of CNT fibers are dependent on the CNT aspect ratio and phase behavior. The phase behavior of CNTs is well described by the CNT aspect ratio, such that the isotropic-to-nematic phase transition behaves accordingly to Onsager’s classical theory for rigid rods. In this work, we study the effect of CNT length and diameter polydispersity on the aspect ratio, the phase behavior, and the macroscopic electrical and mechanical properties of CNT fibers. The effect of high polydispersity in CNT solutions has not been previously reported and it is not yet fully understood. <br/>Two types of CNTs, high aspect ratio (rod length divided by rod diameter L/D) CNTs, and low aspect ratio are mixed in different weight fractions. Transmission electron microscopy, cross-polarized optical microscopy, and extensional rheometry to characterize the phase behavior and viscosity-averaged effective aspect ratio of these bimodal CNT solutions. Finally, CNT fibers are spun via wet spinning to determine their macroscopic electrical and mechanical properties. The results show how the fraction of long-to-short tubes in solution affects the isotropic-to-nematic phase transition and the solution effective aspect ratio as determined by capillary thinning extensional viscosity measurements. These predictions are key to better understanding and optimizing the properties of macroscopic CNT materials made from polydisperse solutions at high concentrations.

Effective aspect ratio, phase behavior, and macroscopic fiber properties of polydisperse, bimodal carbon nanotube solutions

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