Directional sensing based on flexible aligned carbon nanotube film nanocomposites

Abstract

The electrical behaviors under mechanical deformation of an aligned single-walled carbon nanotube (SWCNT) film nanocomposite have been systematically investigated in this work. Electrical signals along the CNT axis (‖) and perpendicular to the CNT axis (⊥) follow a specific pattern, which enables the mechanical motion to be determined by vector analysis of such signals. The unique electrical behaviors of the sandwiched nanocomposites originate from the anisotropic characteristics of the CNT films. By combining in situ mechanical investigation with a coarse-grained molecular dynamics simulation, the shearing effect between SWCNTs is found to play a key role in stress-transfer along the ‖ direction, resulting in arc-shape cracks, while the peeling effect is dominant along the ⊥ direction, leading to unifom SWCNT bar bridging at cracks. The fabricated CNT based sandwiched nanocomposite is believed to have great potential in building flexible all-direction sensors.

Highly Aligned, Anisotropic Carbon Nanofiber Films for Multidirectional Strain Sensors with Exceptional Selectivity

“…One strategy is to utilize the prestrained metal nanowires with percolation networks to distinguish different off‐axis angles . Another strategy is to use aligned conductive fillers, such as aligned carbonized cellulose fibers, aligned carbon nanotubes (CNTs), and aligned spiropyran fibers, to realize independent responses to the strains applied in different directions. An alternative strategy is to prepare the strain sensors using stiffness‐variant polymer substrates to distinguish multidirectional strains, which showed a maximum gauge factor (GF) difference of ≈20 between the perpendicular and parallel directions.…”

Anisotropic, Wrinkled, and Crack-Bridging Structure for Ultrasensitive, Highly Selective Multidirectional Strain Sensors

“…However, these crack-based sensors suffered from very limited stretchability of less than 20% [33,34]. An alternative strategy is to introduce aligned structures as conductive components, such as aligned CNTs or CNT/graphene hybrids [21,[35][36][37][38][39][40], aligned carbon nanofibers (CNFs) [30], vertically aligned graphene [41], and oriented carbonized cellulose fibers [42]. These sensors featured immense stretchability (> 200%) in the alignment direction, while the linearity and sensitivity were relatively low with GFs usually less than 100.…”

“…These sensors featured immense stretchability (> 200%) in the alignment direction, while the linearity and sensitivity were relatively low with GFs usually less than 100. Such low GFs arising from the sliding between the aligned conducting fillers without creating cracks also resulted in low selectivity of less than 2 at strains below 5%, inadequate to differentiate the loading directions [35,37,[42][43][44]. These limitations impede their applications in wearable electronics and artificial skins which require accurate tracking of multiaxial strains with wide sensing ranges over 100% strain [26,45].…”

Strategies for Designing Stretchable Strain Sensors and Conductors

“…To address this issue, many efforts have been devoted to the development of anisotropic sensors . One strategy is to make the sensors into an orthogonal structure .…”

“…Alternatively, intrinsically anisotropic conductive networks formed by aligned conductive materials or prestrained nanomaterial network have been designed to achieve independent responses to strains applied in different directions . For instance, Lee et al developed anisotropic strain sensors based on highly aligned CNFs.…”