Abstract Auxetic materials showing a negative Poisson’s ratio can offer unusual sensing capabilities due to drastic percolation changes. This study presents the capacitive response of wet-fractured carbon nanotube paper composites in exposure to humidity. A strained composite strip is fractured to produce numerous cantilevers consisting of cellulose fibers coated with carbon nanotubes. During stretching, the thin composite buckles in the out-of-plane direction, which causes auxetic behavior to generate the radially structured electrodes. The crossbar junctions forming among the fractured electrodes significantly increase capacitance and its response to humidity as a function of sensor widths. The molecular junctions switch electric characteristics between predominantly resistive- and capacitive elements. The resulting capacitive response is characterized for humidity sensing without the need for an additional absorption medium. The normalized capacitance change (ΔC/C 0 ) exhibits a sensitivity of 0.225 within the range of 40 ∼ 80% relative humidity. The novel auxetic behavior of a water-printed paper-based nanocomposite paves the way for inexpensive humidity and sweat sensors.
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Electromechanical coupling of isotropic fibrous networks with tailored auxetic behavior induced by water-printing under tension
Understanding the electromechanical coupling of auxetic materials offers unique opportunities to enhance the sensitivity of piezoresistive sensors. Reports on the auxetic behavior of random fiber networks have been relatively scarce due to their less pronounced Poisson's expansions than other auxetic designs adapting periodically arranged structures. In this study, the auxetic response of hierarchical pulp-carbon nanotube networks is tailored through the localized tensional micro-fracture initiated by water-printing. The interfacial junctions among multiwalled carbon nanotubes (MWCNTs) and cellulose fibers are disintegrated and reorganized to induce the buckling of a wet CNT paper composite (CPC) network. The Poisson's ratio of −49.5 is achieved at the water-printed region. The resulting piezoresistive properties of CPC sensors exhibit high sensitivity (3.3 kPa −1 ) over a wide dynamic range (6–500 000 Pa). The novel auxetic behavior of water-printed CPC paves the way for high performance and inexpensive wearable devices.
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- Award ID(s):
- 1927623
- NSF-PAR ID:
- 10300371
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 9
- Issue:
- 13
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 4544 to 4553
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0TC05526C
