Piezoresistive Effect in Carbon Nanotube Fibers

Abstract

The complex structure of the macroscopic assemblies of carbon nanotubes and variable intrinsic piezoresistivity of nanotubes themselves lead to highly interesting piezoresistive performance of this new type of conductive material. Here, we present an in-depth study of the piezoresistive effect in carbon nanotube fibers, i.e., yarnlike assemblies made purely of aligned carbon nanotubes, which are expected to find applications as electrical and electronic materials. The resistivity changes of carbon nanotube fibers were measured on initial loading, through the elastic/plastic transition, on cyclic loading and on stress relaxation. The various regimes of stress/strain behavior were modeled using a standard linear solid model, which was modified with an additional element in series to account for the observed creep behavior. On the basis of the experimental and modeling results, the origin of piezoresistivity is discussed. An additional effect on the resistivity was found as the fiber was held under load which led to observations of the effect of humidity and the associated water adsorption level on the resistivity. We show that the equilibrium uptake of moisture leads to the decrease in gauge factor of the fiber decrease, i.e., the reduction in the sensitivity of fiber resistivity to loading.

Electrically Stable Carbon Nanotube Yarn Under Tensile Strain

“…The GF of our asmade CNT yarn, found approximately 0.15, is the smallest value among the CNT yarn GFs in the literature to date [16]- [20]. The improvements in the synthesis of the CNT yarn including the use of a capstan rods system and heat treatment are considered to be the decisive factors for the electrical stability of the CNT yarn.…”

Localized Detection of Damage in Laminated Composite Materials Using Carbon Nanotube Yarn Sensors

“…The CNT yarns composed of one thread have a diameter of about 29 μm and a corresponding SEM image is shown in Figure 1(b). CNT yarns exhibit a piezoresistive response that depends on the exact construction of the material including the nanotube diameter, length and chirality, twist angle of the yarn, fabrication technique and other yarn characteristics [20,21]. The response of unconstrained 1-thread yarns subjected to quasi-static uniaxial tension loading exhibits a negative piezoresistivity [14].…”

Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint

“…After fabrication, the CNT yarn is spun around a spool for storing and handling purposes. Piezoresistivity is a unique and the most important property of the CNT yarns for their application as sensors [11][12][13][14][15][16][17][18]. From a microstructural perspective, for low strain levels (< 2 %), metallic nanotubes play a vital role in the change of the electrical resistance [1,11].…”

“…It is said that the bundles of carbon nanotubes untwist during loading and contact length decreases (the density of CNT yarns per unit length decreases), which leads to the increase in resistance. In contrast, the electrical resistance decreases during the unloading segments [12,14,15]. In addition, a decrease in resistance due to inter-tube/inter-bundle slippage (inelastic shear motion) caused by yarn's relaxation and structural reformation during the loading segments, and a continuous decrease in resistance during unloading as the yarn recovers its (conductive) structure [16].…”