Ultrahigh strength, modulus, and conductivity of graphitic fibers by macromolecular coalescence

Abstract

Theoretical considerations suggest that the strength of carbon nanotube (CNT) fibers be exceptional; however, their mechanical performance values are much lower than the theoretical values. To achieve macroscopic fibers with ultrahigh performance, we developed a method to form multidimensional nanostructures by coalescence of individual nanotubes. The highly aligned wet-spun fibers of single- or double-walled nanotube bundles were graphitized to induce nanotube collapse and multi-inner walled structures. These advanced nanostructures formed a network of interconnected, close-packed graphitic domains. Their near-perfect alignment and high longitudinal crystallinity that increased the shear strength between CNTs while retaining notable flexibility. The resulting fibers have an exceptional combination of high tensile strength (6.57 GPa), modulus (629 GPa), thermal conductivity (482 W/m·K), and electrical conductivity (2.2 MS/m), thereby overcoming the limits associated with conventional synthetic fibers.

Ultrastrong Hybrid Fibers with Tunable Macromolecular Interfaces of Graphene Oxide and Carbon Nanotube for Multifunctional Applications

“…[ 12 , 24 ] In practice, the doped CSA in the CNTs could be removed by heat treatment at 1400 °C or higher, at which time the density and electrical conductivity gradually decrease. [ 15 ] In the case of G‐CNT fibers, the graphitic layers can also contribute to the density increase.…”

“…[ 7 , 8 , 9 , 10 ] However, the bulk properties of CNT‐ or graphene‐based assemblies are an obstacle to exploiting the desirable properties of individual CNT and graphene particles, because of the imperfect alignment of particles, the presence of pores, and the limited connectivity of elements in the assemblies. [ 6 , 7 , 11 , 12 ] To address these problems, many studies have been conducted to improve fiber properties, using post‐treatment processes, [ 13 , 14 , 15 , 16 ] structural approaches, [ 6 , 14 , 15 , 16 , 17 ] and processing methods [ 11 , 12 , 18 ] for individual elements or assemblies.…”

“…[ 3 , 11 , 12 ] In practice, wet‐spun CNT fibers formed using a CSA have excellent macroscopic properties. [ 11 , 12 , 15 , 22 ] However, the properties of the CNT fibers are highly dependent on the length (aspect ratio) of synthesized CNTs. [ 22 , 23 , 24 ] Therefore, a combination of multidimensional structures can be considered to improve the properties of structural assemblies in restricted synthetic CNTs.…”

“…[ 17 , 19 ] Recently, we reported on high‐performance CNT fibers with multidimensional structures assembled by macromolecular coalescence of nanotubes. [ 15 ]…”

Excluded Volume Effect on the Extensional Rheology of Carbon Nanotubes: A Mesoscopic Theory

“…Wet spinning is a strong candidate for achieving exceptional mechanical and electrical properties of carbon nanotubes (CNTs) on a macroscopic scale. − The extensional rheology of the liquid crystalline (LC) phase of CNTs is important to obtain the desired properties of the CNT fiber. CNTs form an LC state above a critical concentration in strong acids, such as sulfonic and chlorosulfonic acid (CSA). − , The orientational shear viscosities of the LC phases of CNTs and graphene oxides (GOs) are analogous to those of polydomain LCs. , However, there is a clear difference between LC nanocarbons and pure LCs in terms of elasticity. ,, For pure LCs, the wide orientation spread of the directors during flow narrows in the equilibrium state with the help of Frank elasticity at a particular shear rate range. − In the LC phases of CNTs and GOs, an elastic force acts in the direction opposite the Frank elastic force in the extensional flow (Figure ).…”