Flexible conductive polymer composite (CPC) fibers that
show large
changes in resistance with deformation have recently gained much attention
as strain-sensing components for future wearable electronics. However,
the electrical resistance of these materials decays with time during
dynamic cyclic loading, a deformation performed to simulate their
real application as strain sensors. Despite the extensive research
on CPC fibers, the mechanism leading to this decay in the electromechanical
response under repetitive cycles remains unreported. Herein, this
behavior is investigated using fiber-based strain sensors wet spun
from thermoplastic polyurethane (TPU) consisting of a carbonaceous
hybrid conductive filler system of carbon black (CB) and carbon nanotubes
(CNTs). We found electrical viscosity to predict the observed electromechanical
resistance decay. This implies that cycling these materials enables
the relaxation of both the polymer chains and the conductive network.
In addition, the resulting piezoresistive fibers are sensitive to
deformation in the region of low strain (gauge factor of 6.0 within
3.0% strain), remain conductive under 280.5% deformation, and are
stable for more than 2000 cycles. Finally, we demonstrate the potential
of TPU/CB-CNT fibers as strain sensors for monitoring human motion.
Piezoresistive fibers with large working factors remain of great interest for strain sensing applications involving large strains, yet difficult to achieve. Here, we produced strain-sensitive fibers with large working factors by dip-coating nanocomposite piezoresistive inks on surface-modified polyether block amide (PEBA) fibers. Surface modification of neat PEBA fibers was carried out with polydopamine (PDA) while nanocomposite conductive inks consisted of styrene−ethylene− butylene−styrene (SEBS) elastomer and carbon black (CB). As such, the deposition of piezoresistive coatings was enabled through nonconventional hydrogen-bonding interactions. The resultant fibers demonstrated well-defined piezoresistive linear relationships, which increased with CB filler loading in SEBS. In addition, gauge factors decreased with increasing CB mass fractions from ∼15 to ∼7. Furthermore, we used the fatigue theory to predict the endurance limit (C e ) of our fibers toward resistance signal stability. Such a piezoresistive performance allowed us to explore the application of our fibers as strain sensors for monitoring the movement of finger joints.
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