Studies Of Morphology Control Of Electrospun Nanofibers By Opposite Voltage

This work was focused on the morphology control of electrospun nanofibers for nano materials. Several helical nanofibers, ropes, and3D balls were made by the alternated method with the assisted of oppositely charged collector and opposite spinneret. In addition, the electrospinning condition were also discussed in this thesis.(1) Double helical microropes of polyvinylpyrrolidone (PVP) with diameters less than10μm and lengths up to5cm were fabricated by a new electrospinning technique. Different from the typical electrospinning setup, a negatively charged rotating collector tip was used in this work, so that the two jets from two positively charged spinnerets were induced to two bundles that met at the rotating collector tip, leading to the formation of microropes. The pitch of microropes could be monitored by simply adjusting the distance of two spinnerets.(2) We developed a simple approach to design and fabricate precisely controlled coiled nanofibers via the micromanufacture of electrospun nanofibers (MENS). The fabrication set-up was specially designed so that one stream of polyvinyl pyrrolidone (PVP) sol with ferric nitrate was electrospun onto a fiber bundle. This bundle acted as an axis that was collected between two opposite rotating needles while another stream of PVP sol, containing copper nitrate, was electrospun around the fiber bundle axis to form a coil. By altering the elements in the precursor solution, copper microsolenoids with magnetite (Fe3O4) cores were fabricated followed by annealing and deoxidation.(3) A fabrication setup was specially designed so that one stream of sol of polyvinyl pyrrolidone (PVP) was electrospun to form a bundle of fibers acted as an axis that was collected between two rotating needles while another stream of PVP sol containing copper nitrate was electrospun around the fiber bundle axis to form a coil. It was turned into a coiled ribbon upon the treatment in moisture. After calcination and reduction, a helical micro-coil of nano copper ribbon was produced, which diameter and pitch could be monitored. The width and thicknesses of ribbon could also be varied by controlling the diameter of coiled fiber and treatment time in moisture.(4) We describe the formation of micro spiral structures resulting from buckling instabilities of an electro jet of a nanoscale polymer fiber of polyvinglpyrrolidone-Cu(NO3)2(PVP-Cu(NO3)2) sol). We control the morphologies of the fibers into spiral fibers, and free-standing hollow cylinders by connecting an opposite high voltage supply (-5to-10kV) on the collector. The microstructured surfaces were observed by scanning electron microscope (SEM). SEM analysis revealed the presence of spirals with diameters of approximately20to30μm. The structures formed by the nanofibers could be used in diverse fields of nanotechnology, such as micro planar inductor and nanochannels.(5) Three-dimensional (3D) porous frameworks with nano/micro structured materials are promising in broad applications. However, conventional electrospinning process is de facto limited to the surface depositions of2D nanofibers mats. Here, thea novel methodology of makingcreating3D nanofibers scaffolds is presented, which featuresing self-neutralization and self-assembly of electrospun nanofibers by means of dual electrospinning from two oppositely charged polymer jets. By counterbalancing the gravity of intertwined jets, thanks to a controllable upward air flow from a tunable heat source, mass production of3D nanofibers materials can be realized. Among various applications, such as to tissue engineering scaffolds, material separation diaphragms, energy storage systems, and catalyst materials, etc., we experimentally measure the sound absorption coefficients of the3D nanofibers scaffolds in the low frequency range, and observe obvious enhancement to the absorption performance from400to900Hz, comparing with commercial sound-absorbing cotton.(6) Surface hybridization with carbon nanolayers of TiO2nanofibers with length in centimeters were fabricated. Comparing with TiO2nanofibers, the carbon layer covered TiO2nanofibers photocatalyst presented a higher photocatalytic activity under ultraviolet (UV) irradiation for the degradation of organics (methylene blue). TiO2modification with carbon nanolayers to increase substrate adsorption in the vicinity of the photocatalytic sites and the high migration efficiency of photoinduced electrons at the carbon/TiO2interface lead to a photocatalyst with enhanced efficiency. Photostability kept after five times recycled under UV irradiation.