For flexible strain sensors, the optimization between
sensitivity
and working range is a significant challenge due to the fact that
high sensitivity and high working range are usually difficult to obtain
at the same time. Herein, a breathable flexible strain sensor with
a double-layered conductive network structure was designed and developed,
which consists of a thermoplastic polyurethane (TPU)/carbon nanotube
(CNT) layer (as a substrate layer) and a Ag nanowire (AgNW) layer.
The TPU/CNT layer is made of electrospinning TPU with CNTs deposited
onto the surface of TPU fibers, and the flexible TPU/CNT mat guarantees
the integrity of the conductive path under a large strain. The AgNW
layer was prepared by depositing different amounts of AgNWs on the
surface of the TPU/CNT layer, and the high-conductivity AgNWs offer
a low initial resistance. Benefitting from the synergistic two-layer
structure, the as-obtained flexible strain sensor exhibits a very
high sensitivity (up to 1477.7) and a very wide working range (up
to 150%). Besides, the fabricated sensor exhibits fast response (88
ms), excellent dynamical stability (7000 cycles), and excellent breathability.
The working mechanism of the strain sensor was further investigated
using various techniques (microscopy, equivalent circuit, and thermal
effects of current). Furthermore, the as-fabricated flexible strain
sensors accurately detect the omnidirectional human motions, including
subtle and large human motions. This work provides an efficient approach
to achieve the optimization between high sensitivity and large working
range of strain sensors, which may have great potential applications
in health monitoring, body motion detection, and human–machine
interactions.
Ultrafine composite fibers consisting of a thermoplastic polyurethane solid-solid phase-change material and organic lanthanide luminescent materials were prepared through a parallel electrospinning technique as an innovative type of ultrafine, dual-functional fibers containing phase-change and luminescent properties. The morphology and structure, thermal energy storage, and luminescent properties of parallel electrospun ultrafine fibers were investigated. Scanning electron microscopy (SEM) images showed that the parallel electrospun ultrafine fibers possessed the desired morphologies with smaller average fiber diameters than those of traditional mixed electrospun ultrafine fibers. Transmission electron microscopy (TEM) images revealed that the parallel electrospun ultrafine fibers were composed of two parts. Polymeric phase-change materials, which can be directly produced and spun, were used to provide temperature stability, while a mixture of polymethyl methacrylate and an organic lanthanide complex acted as the luminescent unit. Differential scanning calorimetry (DSC) and luminescence measurements indicated that the unique structure of the parallel electrospun ultrafine fibers provides the products with good thermal energy storage and luminescence properties. The fluorescence intensity and the phase-change enthalpy values of the ultrafine fibers prepared by parallel electrospinning were respectively 1.6 and 2.1 times those of ultrafine fibers prepared by mixed electrospinning.
A polyethylene terephthalate nano porous luminescence fiber (PNPLF) was prepared through electrospun technology. The SEM and TEM images show that the surfaces of the fibers are covered with pores. The diameter of the fiber is 250-500 nm, and the diameter of the pores is 20-180 nm. The water and oil contact angles of PNPLF are 135° and 27°, respectively. The oil absorption value of the as-prepared PNPLF achieves 135 g/g and has a good oil absorption function. The as-prepared PNPLF has good luminescence properties and fluorescent-indicating function. Even trace amounts of oil can also cause obvious change of fluorescence intensity of PNPLF which has a good stability from 20 °C to 70 °C. The breaking stress of yarn of PNPLF reaches 117cN. Furthermore, the good mechanical properties and thermal properties of PNPLF provide important basic conditions for their wide applications.
Li–S batteries present great potential to realize
high-energy-density
storage, but their practical implementation is severely hampered by
the notorious polysulfide shuttling and the sluggish redox kinetics.
While rationally designed redox mediators can optimize polysulfide
conversion, the efficiency and stability of such a mediation process
still remain formidable challenges. Herein, a strategy of constructing
a “dual mediator system” is proposed for achieving efficient
and durable modulation of polysulfide conversion kinetics by coupling
well-selected solid and electrolyte-soluble mediators. Theoretical
prediction and detailed electrochemical analysis reveal the structure–activity
relationships of the two mediators in synergistically optimizing the
redox conversions of sulfur species, thus achieving a deeper mechanistic
understanding of a function-supporting mediator system design toward
sulfur electrochemistry promotion. Specifically, such a dual mediator
system realizes the bridging of full-range “electrochemical
catalysis” and strengthened “chemical reduction”
processes of sulfur species as well as greatly suppressed mediator
deactivation/loss due to the beneficial interactions between each
mediator component. Attributed to these advantageous features, the
Li–S batteries enable a slow capacity decay of 0.026% per cycle
over 1200 cycles and a desirable capacity of 8.8 mAh cm–2 with 8.2 mg cm–2 sulfur loading and lean electrolyte
condition. This work not only proposes an effective mediator system
design strategy for promoting Li–S battery performance but
also inspires its potential utilization facing other analogous sophisticated
electrochemical conversion processes.
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