Showing papers by "Shaoli Fang published in 2017"

Harvesting electrical energy from carbon nanotube yarn twist

Abstract: Mechanical energy harvesters are needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. We report carbon nanotube yarn harvesters that electrochemically convert tensile or torsional mechanical energy into electrical energy without requiring an external bias voltage. Stretching coiled yarns generated 250 watts per kilogram of peak electrical power when cycled up to 30 hertz, as well as up to 41.2 joules per kilogram of electrical energy per mechanical cycle, when normalized to harvester yarn weight. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a light-emitting diode and to charge a storage capacitor.

High Power Density Electrochemical Thermocells for Inexpensively Harvesting Low-Grade Thermal Energy.

Abstract: Continuously operating thermo-electrochemical cells (thermocells) are of interest for harvesting low-grade waste thermal energy because of their potentially low cost compared with conventional thermoelectrics. Pt-free thermocells devised here provide an output power of 12 W m-2 for an interelectrode temperature difference (ΔT) of 81 °C, which is sixfold higher power than previously reported for planar thermocells operating at ambient pressure.

A Bi-Sheath Fiber Sensor for Giant Tensile and Torsional Displacements

Abstract: Current research about resistive sensors is rarely focusing on improving the strain range and linearity of resistance–strain dependence. In this paper, a bi-sheath buckled structure is designed containing buckled carbon nanotube sheets and buckled rubber on rubber fiber. Strain decrease results in increasing buckle contact by the rubber interlayer and a large decrease in resistance. The resulting strain sensor can be reversibly stretched to 600%, undergoing a linear resistance increase as large as 102% for 0–200% strain and 160% for 200–600% strain. This strain sensor shows high linearity, fast response time, high resolution, excellent stability, and almost no hysteresis.

Tunable, Fast, Robust Hydrogel Actuators Based on Evaporation-Programmed Heterogeneous Structures

Abstract: The ability to topographically structure and fast controllably actuate hydrogel in two and three dimensions is the key for their promising applications in soft robots, microfluidic valves, cell and drug delivery, and artificial muscles. Inspired by evaporation-induced concentration differentiation phenomenon in the production process of beancurd sheet, we introduce a facile one-step evaporation process to create laminated layer/porous layer heterogeneous structure within graphene oxide-clay-poly(N-isopropylacrylamide) hydrogel in vertical direction and pattern the heterogeneous structure in lateral direction to form tunable, fast, and robust hydrogel actuators. The laminated layer/porous layer architecture is highly stable and robust without possibility of delamination. The evaporation-programmed heterogeneous structures tune thermoresponsive actuations from global bending/unbending for global heterogeneous structure to local bending/unbending and site-specific folding/unfolding for segment-patterned hete...

Polar-Electrode-Bridged Electroluminescent Displays: 2D Sensors Remotely Communicating Optically

Abstract: A novel geometry for electroluminescent devices, which does not require transparent electrodes for electrical input, is demonstrated, theoretically analyzed, and experimentally characterized. Instead of emitting light through a conventional electrode, light emission occurs through a polar liquid or solid and input electrical electrodes are coplanar, rather than stacked in a sandwich configuration. This new device concept is scalable and easily deployed for a range of modular alternating-current-powered electroluminescent light sources and light-emitting sensing devices. The polar-electrode-bridged electroluminescent displays can be used as remotely readable, spatially responsive sensors that emit light in response to the accumulation and distribution of materials on the device surface. Using this device structure, various types of alternating current devices are demonstrated. These include an umbrella that automatically lights up when it rains, a display that emits light from regions touched by human fingers (or painted upon using a mixture of oil and water), and a sensor that lights up differently in different areas to indicate the presence of water and its freezing. This study extends the dual-stack, coplanar-electrode device geometry to provide displays that emit light from a figure drawn on an electroluminescent panel using a graphite pencil.

A facile one-step approach for the fabrication of polypyrrole nanowire/carbon fiber hybrid electrodes for flexible high performance solid-state supercapacitors.

Abstract: Wearable electronics are in high demand, requiring that all the components are flexible. Here we report a facile approach for the fabrication of flexible polypyrrole nanowire (NPPy)/carbon fiber (CF) hybrid electrodes with high electrochemical activity using a low-cost, one-step electrodeposition method. The structure of the NPPy/CF electrodes can be easily controlled by the applied electrical potential and electrodeposition time. Our NPPy/CF-based electrodes showed high flexibility, conductivity, and stability, making them ideal for flexible all-solid-state fiber supercapacitors. The resulting NPPy/CF-based supercapacitors provided a high specific capacitance of 148.4 F g-1 at 0.128 A g-1, which is much higher than for supercapacitors based on polypyrrole film/CF (38.3 F g-1) and pure CF (0.6 F g-1) under the same conditions. The NPPy/CF-based supercapacitors also showed high bending and cycling stability, retaining 84% of the initial capacitance after 500 bending cycles, and 91% of the initial capacitance after 5000 charge/discharge cycles.

Actuating textiles containing polymer fiber muscles

Abstract: A smart (intelligent) textile that can control its porosity, shape, texture, loft, stiffness, or color by temperature change or moisture absorption by using polymer fiber torsional and tensile actuators This temperature change can be due to a change in ambient temperature or by an external stimulus, such as electrothermal heating Mechanisms to accomplish this include (a) direct actuation (contraction or expansion) of polymer fiber actuators in a textile structure (b) rotation of polymer fiber actuators helically wrapped around warp and/or weft yarns in a textile structure; (c) rotation of chenille type or ribbon-like warp (or weft) ends by polymer fiber torsional actuators; (d) contraction or expansion of piles or loops in a chenille type fancy yarn produced by using mandrel actuators as pile or loop part of the yarn; (e) buckling of warp (or weft) yarns by contraction of tensile polymer fiber actuators; (f) decrease in yarn diameter by a twisting effect of polymer fiber actuators; (g) contraction or expansion of segmented mandrel actuators with core filament, wire or yarns; or (h) rotation of differentially dyed polymer fiber actuators for color changing textiles

Coiled, twisted nanofiber yarn and polymer fiber torsional actuators

Abstract: Actuators (artificial muscles) comprising twist-spun nanofiber yarn or twist-inserted polymer fibers generate torsional actuation when powered electrically, photonically, chemically, thermally, by absorption, or by other means. These artificial muscles utilize coiled yarns/polymer fibers and can be either neat or comprising a guest. In some embodiments, the torsional fiber actuator includes a first polymer fiber (exhibiting a first polymer fiber diameter) and a torsional return spring in communication with the first polymer fiber. The first polymer fiber is configured to include a first plurality of twists in a first direction to produce a twisted polymer fiber. The first polymer fiber is further configured to include a plurality of coils in the twisted polymer fiber in a second direction each coil having a mean coil diameter. In some embodiments, the torsional nanofiber actuator includes a first carbon nanofiber yarn (having a yarn diameter) and a torsional return spring in communication with the first carbon nanofiber yarn. The first carbon nanofiber yarn includes a plurality of twists in a first direction to produce a twisted carbon nanofiber yarn. The first carbon nanofiber yarn further includes a plurality of coils in the twisted carbon nanofiber yarn, with each coil having a mean coil diameter greater than the yarn diameter.