Yun Ze Long

Electrical Conductivity Studies on Individual Conjugated Polymer Nanowires: Two-Probe and Four-Probe Results

Two- and four-probe electrical measurements on individual conjugated polymer nanowires with different diameters ranging from 20 to 190 nm have been performed to study their conductivity and nanocontact resistance. The two-probe results reveal that all the measured polymer nanowires with different diameters are semiconducting. However, the four-probe results show that the measured polymer nanowires with diameters of 190, 95–100, 35–40 and 20–25 nm are lying in the insulating, critical, metallic and insulting regimes of metal–insulator transition, respectively. The 35–40 nm nanowire displays a metal–insulator transition at around 35 K. In addition, it was found that the nanocontact resistance is in the magnitude of 104Ω at room temperature, which is comparable to the intrinsic resistance of the nanowires. These results demonstrate that four-probe electrical measurement is necessary to explore the intrinsic electronic transport properties of isolated nanowires, especially in the case of metallic nanowires, because the metallic nature of the measured nanowires may be coved by the nanocontact resistance that cannot be excluded by a two-probe technique.

Fabrication of Nano-branched Coaxial Polyaniline / Polyvinylidene Fluoride Fibers via Electrospinning for Strain Sensor

Soft conductive elastomer materials have wide potential applications in material science and electronic engineering. Through electrospinning and in-situ polymerization, a kind of well-organized coaxial polyaniline/polyvinylidence fluoride (PANI/PVDF) microfibers with conductivity about 0.6 S/cm were fabricated, which combined the advantages of conducting polymer and elastic material. It is found that the resistance of the fibers was changed with the curvature variation. The results indicate that the PANI/PVDF microfibers could be used as strain sensor with high flexibility, high sensitivity, and stable repeatability.

Aligned Nanofiber Arrays and Twisted Nanofiber Ropes via Electrospinning with Two Frames Collector

A modified electrospinning setup with two-grounded-frame collector is proposed to fabricate aligned fiber arrays and fiber ropes. In this setup, two frames are placed under the spinneret, with the outer frame rotated with an electromotor and the inner frame hold still in a horizontal direction. Aligned nanofiber arrays can be collected rapidly on the inner frame. Influence of included angle and motor rotating speed on the arrays is discussed. In addition, through rotating one side of the inner frame, twisted fiber ropes with diameter 30~40 μm and length of 12 cm are obtained. Mechanical properties of the individual nanofiber ropes are also measured and discussed.

Preparation and Electrochemical Properties of LiMn2O4 Nanofibers via Electrospinning for Lithium Ion Batteries

LiMn2O4 nanofibers were prepared via electrospinning and followed by calcination. The surface morphology of as-spun and pure LiMn2O4 nanofibers was characterized by a scanning electron microscope (SEM) with an average diameter of 180 nm. After calcination at 800 °C in air for 5 h, charge/discharge capacity of pure LiMn2O4 nanofibers was measured in the potential range of 3.0 to 4.3 V. Battery testing showed that LiMn2O4 have a high discharge capacity of 80 mAh/g and 85% of the initial charge capacity was maintained for 5 cycles.

Ultrasensitive Fluorescence Lifetime Tuning in Patterned Polymer Composite Nanofibers with Plasmonic Nanostructures for Multiplexing

Regulating fluorescence lifetime of lanthanide nanocomposites is highly desired for optical multiplexing applications, for instance, security printing, anticounterfeiting, and data storage. Herein, sensitive fluorescence lifetime tuning in nanocomposite fibers is reported which are composed of silica-coated gold nanorods assembled in Eu-polystyrene nanofibers. The prepared nanofibers possess unique properties of tunable fluorescence lifetime and distinct textured patterns together with superior flexibility and superhydrophobicity. In a single 612 nm emission channel, over ten different populations of fluorescence lifetime from the range of 322-551 µs are harvested. Thanks to the tunable fluorescence lifetime and different textured patterns, a security pattern to demonstrate optical multiplexing applications is designed. The security pattern hides the real information of 69 in a noticeable scene that shows fake information 8 under UV radiation or 13 by only watching their pattern structures.

Fabrication and Photoelectric Properties of La-Doped ZnO Nanofibers via Electrospinning

La-doped ZnO nanofibers were fabricated via electrospinning and calcination at 800°C. The surface morphology and crystal structure of the La-doped ZnO nanofibers were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The photoelectric properties of La-doped ZnO nanofibers were also investigated. It was found that the photoelectric current increased obviously under light illumination (308 nm and 365 nm). However, the photocurrent reduced with increasing La-doping level, which may be ascribed to the increased defects inducing by La-doping.

Ultrafast Response Humidity Sensor Based on Electrospun Porous BaTiO3 Nanofibers

Nanocrystalline and porous barium titanate (BaTiO3) nanofibers with diameter 200-400 nm were synthesized via electrospinning and followed calcinations. The morphology and microstructure of the nanofibers were characterized using field emission scanning electron microscope, X-ray diffractometer and transmission electron microscope, respectively. And the electrical and humidity sensing properties of the nanofibers were also measured. The results reveal that the BaTiO3 nanofibers have a conductivity of about 0.3 S/cm, and show an ultrafast response time (~0.7 s) and a recovery time (~0.4 s) to humidity at room temperature. In addition, the sensing mechanism was also discussed briefly based on its nanocrystalline and porous microstructure of the electrospun material.

Electrical Properties of Electrospun Flexible and Stretchable PVDF/PANI Nanoropes

Aligned poly (vinylidene fluoride) (PVDF) nanofibers and the nanoropes have been fabricated via a novel electrospinning technique. And then conducting polyaniline (PANI) was coated on the surfaces of the nanoropes using an in situ chemical oxidative polymerization method. It is found that the conductivity increased drastically at first and then tended to be saturation in the polymerization process. In addition, the flexibility and stretchability of the composites have been measured: With an increase of bending curvature and tensile strain, the conductivity rose at the beginning because the fibers among the nanoropes get tight; and then the conductivity dropped, which may due to the PANI layer broke and becomes discontinuous with the adding stress.

Fabrication of Microfibrous Patterns via Electrospinning

Using patterned conductive and insulating collection devices, fibrous patterns from polyvinyl pyrrolidone were fabricated by electrospinning. Considering that the electrospun fibers tend to deposit along the direction of electric field line, when conductive patterned template is used as collector during electrospinning, the as-spun fibers tend to assemble onto the conductive grids, whereas the dropping fibers prefer to avoid insulation grid by concentrating toward the surface of the Al foil when an insulating grid based on Al foil is used as collector.

Fabrication and Formation Mechanism of Electrospun Spatially Defined Fibrous Patterning Structures on Conductive and Insulating Substrates

Besides the conductive patterning substrate, spatially well-defined microfibrous architectures can also be electrospun by using an insulating topographically structured collector (e.g. a nylon fabric). In both cases, it is proposed that the formation of the electrospun microfibrous patterns can be ascribed to the re-distribution of static electric field whenever collectors with different topography are introduced. Moreover, a series of simulation of the static electric field for various collectors (e.g. flat Al foil, conductive and insulating patterned substrates) have been systematically made to illustrate the formation mechanism, respectively. Our results are considered to warrant further scientific understanding on the formation of electrospun microfibrous patterning constructs, and helpful for easy generation of spatially defined architectures which have applications in a variety of areas such as tissue engineering, cell adhesion, proliferation and migration, etc.