Electrically conductive polymer composite-based smart strain sensors with different conductive fillers, phase morphology, and imperative features were reviewed.
Thermoplastic polyurethane (TPU) based conductive polymer composites (CPCs) with a reduced percolation threshold and tunable resistance-strain sensing behavior were obtained through the addition of synergistic carbon nanotubes (CNT) and graphene bifillers. The percolation threshold of graphene was about 0.006 vol% when the CNT content was fixed at 0.255 vol% that is below the percolation threshold of CNT/TPU nanocomposites. The synergistic effect between graphene and CNT was identified using the excluded volume theory. Graphene acted as a 'spacer' to separate the entangled CNTs from each other and the CNT bridged the broad gap between individual graphene sheets, which was beneficial for the dispersion of CNT and formation of effective conductive paths, leading to better electrical conductivity at a lower conductive filler content. Compared with the dual-peak response pattern of the CNT/TPU based strain sensors, the CPCs with hybrid conductive fillers displayed single-peak response patterns under small strain, indicating good tunability with the synergistic effect of CNT and graphene. Under larger strain, prestraining was adopted to regulate the conductive network, and better tunable single-peak response patterns were also obtained. The CPCs also showed good reversibility and reproductivity under cyclic extension. This study paves the way for the fabrication of CPC based strain sensors with good tunability.
Ingenious
microstructure design and a suitable multicomponent strategy
are still challenging for advanced electromagnetic wave absorbing
(EMA) materials with strong absorption and a broad effective absorption
bandwidth (EAB) at thin sample thickness and low filling level. Herein,
a three-dimensional (3D) dielectric Ti3C2T
x
MXene/reduced graphene oxide (RGO) aerogel
anchored with magnetic Ni nanochains was constructed via a directional-freezing method followed by the hydrazine vapor reduction
process. The oriented cell structure and heterogeneous dielectric/magnetic
interfaces benefit the superior absorption performance by forming
perfect impedance matching, multiple polarizations, and electric/magnetic-coupling
effects. Interestingly, the prepared ultralight Ni/MXene/RGO (NiMR-H)
aerogel (6.45 mg cm–3) delivers the best EMA performance
in reported MXene-based absorbing materials up to now, with a minimal
reflection loss (RLmin
) of −75.2
dB (99.999 996% wave absorption) and a broadest EAB of 7.3
GHz. Furthermore, the excellent structural robustness and mechanical
properties, as well as the high hydrophobicity and heat insulation
performance (close to air), guarantee the stable and durable EMA application
of the NiMR-H aerogel to resist deformation, water or humid environments,
and high-temperature attacks.
Flexible, lightweight,
robust, and multifunctional characteristics are greatly desirable
for next-generation wearable electromagnetic interference (EMI) shielding
materials. In this work, an alternating multilayered structure with
robust polymer frame layers and directly contacted conducting layers
was designed to prepare high-performance EMI films. Especially, the
multilayered films containing alternating cellulose nanofiber (CNF)
layers and MXene layers are fabricated via a facile and efficient
alternating vacuum filtration approach. Deriving from the mechanical
frame effect acted by CNF layers in, which is capable of preventing
the nanosized “zigzag” crack in MXene layers from growing
to the whole film, the alternating multilayered film (CNF@MXene) revealed
the improved mechanical strength (112.5 MPa) and toughness (2.7 MJ
m–3) compared to both freestanding MXene film and
homogeneous CNF/MXene film. Meanwhile, the directly contacted MXene
layers resulted in the increased electrical conductivity from 2 (homogeneous
CNF/MXene film) to 621–82 S m–1 (CNF@MXene
films). In conjunction with the extra “reflection-absorption-zigzag
reflection” mechanism among the alternating multilayers, CNF@MXene
films demonstrated an exceptional EMI shielding effectiveness of ∼40
dB in the X-band and K-band and high specific shielding effectiveness
up to 7029 dB cm2 g–1 at a thickness
of only 0.035 mm. Besides, the excellent mechanical flexibility ensured
the stable EMI shielding and electrical properties, which can withstand
the folding test more than 1000 times without obvious reduction. Moreover,
the excellent electrical conductivity endows the alternating multilayered
film with an outstanding and steady Joule heating performance, which
could reach more than 100 °C at only 6 V impressed voltage to
within 10 s. As a result, our alternating multilayered film with reinforced
EMI shielding and Joule heating performance is promising in the next-generation
intelligent protection devices applying in cold and complex practical
environments.
Inspired by the ultralight and structurally robust spider webs, flexible nanofibril‐assembled aerogels with intriguing attributes have been designed for achieving promising performances in various applications. Here, conductive polyimide nanofiber (PINF)/MXene composite aerogel with typical “layer‐strut” bracing hierarchical nanofibrous cellular structure has been developed via the freeze‐drying and thermal imidization process. Benefiting from the porous architecture and robust bonding between PINF and MXene, the PINF/MXene composite aerogel exhibits an ultralow density (9.98 mg cm−3), intriguing temperature tolerance from ‐50 to 250 °C, superior compressibility and recoverability (up to 90% strain), and excellent fatigue resistance over 1000 cycles. The composite aerogel can be used as a piezoresistive sensor, with an outstanding sensing capacity up to 90% strain (corresponding 85.21 kPa), ultralow detection limit of 0.5% strain (corresponding 0.01 kPa), robust fatigue resistance over 1000 cycles, excellent piezoresistive stability and reproductivity in extremely harsh environments. Furthermore, the composite aerogel also exhibits superior oil/water separation properties such as high adsorption capacity (55.85 to 135.29 g g−1) and stable recyclability due to its hydrophobicity and robust hierarchical porous structure. It is expected that the designed PINF/MXene composite aerogel can supply a new multifunctional platform for human bodily motion/physical signals detection and high‐efficient oil/water separation.
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