Devices Based On Micro/Nano-fibers And Their Applications

Micro/nano-fiber devices are very important in our society for their wide applicationsin humidity control, special gas monitoring (especially in hydrogen detecting),temperature actuator and wastewater monitoring. Recently, one-dimensional (1D) andquasi-1D nano/micro fibers have been demonstrated to be a candidate for realizing thehigh efficient and low cost sensing devices owing to their unique electrical andthermal transport or mechanical properties on dimensionality and size reduction.Electrospinning technique is most simple and inexpensive for producing nanofibers.With large surface area, fast signal transfer, nano-effect, electrospun nanofibers aregood choices for investigating high performance sensors. Furthermore, as thepotential applications as artificial muscle, fiber based thermal actuator has beengaining great interest in the past a few years. Here, we demonstrated three devices(humidity sensor, hydrogen sensor and thermal actuator) based on nano/micro fibers.1. Both single and multiple nanofibers high-efficiency DC humidity sensorbased on Li+-doped SnO2nanofibers have been demonstrated via electrospinningtechnique and calcinations procedure. Because alkali ions such as Li+or K+are oftenused in fabricating humidity sensors, here LiCl is selected for dopant to improve thesensor characteristics. For14.6at%Li+doped SnO2multiple nanofibers, The responsecurrent increases remarkably with enhancing RH, as the RH increases from33%to85%, the current ranges between11and54μA, and the response-recovery time is4sand1s, respectively. And for14.6at%Li+doped SnO2single nanofiber, the responsecurrent is between2.2×10-8A~96.4×10-8A and the response-recovery time is120sand135s, respectively. And the linear property of the single nanofibers sensor isbetter than pristine SnO2nanofiber sensor and even multiple nanofibers sensor. Thelow cost (working power is only a few microwatts) and excellent humidity sensing properties make both Li+-doped SnO2multiple and single nanofibers DC humiditysensor a good candidate for practical applications.2. High-efficiency hydrogen sensor based on Al-doped and V-doped SnO2nanofbers has been demonstrated via electrospinning technique and calcinationprocedure, respectively. The morphology, structure, and composition of theas-prepared nanofibers are characterized by transmission electron microscopy (TEM),X-ray diffraction (XRD), and energy dispersive X-ray spectrometer (EDX),respectively. XRD analysis indicates Al-SnO2metastable solid solution is formed atthe low concentrations, while the Al2O3-SnO2heterojunction structures can beobtained at high concentrations. Excellent hydrogen sensing properties such as highsensitivity, fast response-recovery behavior, and good selectivity have been obtained.The results prove that the gas performances are affected not only by the additive butalso the state of the additive based on the host material. Compare to the pristine SnO2nanofiber, the response-recovery time has been reduced by50%and the response(Ra/Rg) has been increased by100%.3. The high cost of powerful, large-stroke, high-stress thermal actuator(artificial muscle) fibers has combined with performance limitations, likelow-cycle-life, hysteresis, and low efficiency, to restrict applications. We demonstratethat inexpensive, high-strength polymer fibers used for fishing line and sewing threadcan be easily transformed by extreme twist-insertion and resulting coiling to providefast, scalable, non-hysteretic, long-life tensile and torsional muscles that can contract34%, generate torque of6.5N·m/Kg, lift loads over twice stroke as human muscle’slargest stroke.