Wide‐Range Tunable Dynamic Property of Carbon‐Nanotube‐Based Fibers

Abstract

Carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the non-zero loss tangent (>0.028-0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by the high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest loss tangent, nearly as the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, as similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems.Natural and synthetic fibers are used in many products and play a large role in everyday applications. Their mechanical properties are important both from the point of view of fiber processing in a technological process and their use in the form of final products. Besides the quasi-static properties including the fiber's tensile strength (σ f ), elastic modulus (E f ), and fracture toughness (J f ), the dynamic response to a periodic external signal (displacement or force) can be severe due to the energy dissipation.1 Obviously, frictional effects play a major role in the dynamic response. However, the types of friction differ greatly between a thread, yarn, and fiber due to their different assembly structures.Fiber is usually defined as a hair-like strand of material and is the smallest "visible" unit of a fabric. Natural fibers (cotton, flax, jute, bamboo, kapok, ramie, wool, silk, and spider silk) and synthetic fibers (nylon, glass fiber, cellulose fiber, and carbon fiber) usually have a width (diameter) ranging from several to tens of µm, and a length at least 100 times longer than the width. Yarn is a continuous length of interlocked fibers used for manufacturing textiles.2 At the uppermost structure level, threads are usually made by plying and twisting yarns, for efficient and smooth stitching in sewn products.When carbon nanotubes (CNTs) are assembled into a strand by a spinning process, 3-9 a new man-made or synthetic fiber is formed. A CNT fiber with a diameter of ∼10 µm usually contains more than 10 6 individual CNTs. Such assembly feature is different from those fibers well-known for many years which are usually a solid structure without internal interfaces. CNT fiber can also be considered as a continuous len...

Interfacial Mechanical Behaviors in Carbon Nanotube Assemblies

“…The frequency dependence of loss tangent for the dry-spun CNT fiber, ethylene-glycol-densified CNT fiber, and T300 carbon fiber. 109 CNT fibers, while that for the T300 carbon fiber was nearly zero due to the absence of interfaces. When the CNT fibers were densified by ethylene glycol, the CNTs became constrained, corresponding to reduced loss tangents, see Figure 13.…”

“…CNT fiber can also be considered a continuous length of interlocked "filaments" (CNT bundles), where the bundles are formed during the CNT growth rather than in the spinning process. As I have pointed out recently, 109 although also being called as CNT yarn, CNT fiber is indeed not a yarn because the CNT bundles are not macroscopically processable. On the contrary, the basic components of a yarn, the long and parallel or interlocked filaments, are usually processable objects with a width larger than several micrometers.…”

Understanding the Mechanical and Conductive Properties of Carbon Nanotube Fibers for Smart Electronics

“…In the first period, three fiber spinning methods were developed, which are solution spinning, spinning from a presynthesized vertically aligned CNT forest, and direct spinning from an entangled CNT aerogel while being formed in a high‐temperature reactor . In the following several years, the attention was turned to the mechanisms behind the coagulation process in solution spinning to achieve high electrical performance, structure control and continuous production of aerogel‐spun fibers, and forest‐spun fibers with improved strength and electrical conductivity, as well as advanced dynamic mechanical properties . Meanwhile, potential applications of CNT fibers have been developed, including wearable energy storage and harvesting devices, lightweight wires, and actuators .…”

“…Note that CNT fiber is also called CNT yarn, due to the similarity of twisted structure with the conventional textile yarns. However, as pointed by Zhao et al, the basic component filaments in a CNT fiber are CNT bundles with a diameter of tens of nanometers, which are not macroscopically processable. On the contrary, the basic components in a textile yarn are fibers with a diameter of tens of micrometers, namely, macroscopically processable.…”

“…Owing to the rich intertube contacts, CNT fibers also exhibit excellent vibration damping performance. Hehr et al and Zhao et al used different ways to investigate the damping ratio (a tangent of phase difference tan δ providing information on the relationship between the elastic and inelastic components, namely, E ″ and E ′ for the loss and storage moduli). The results showed that even at a very low vibration frequency (even far below 0.1 Hz), CNT fibers exhibited a damping ratio of 0.028–0.045, while for a carbon fiber, it was nearly zero (≈0.001).…”