Morphology Controlling During Electrospinning And Its Applications

There has been rapidly expanding interest in electrospinning during recent years, owing to its many attractive features, such as its comparatively low-cost and relatively high production rate, its ability to generate materials with large surface area to volume ratios and its applicability to many types of materials. By controlling the electrospinning conditions, various interesting structures with unique properties, including ultrafine nanofibres, beaded nanofibres, porous nanofibres, nanotubes, and nanobelts and three-dimensional architectures, can easily be obtained. It has been a hot topic in the field of materials science, because that some materials with specific nanostructure can often find its unique applications. In this dissertation, solid nanofibres and hollow nanofibres were fabricated by adjusting the competition between the solvent evaporation dynamic and phase separation dynamic. Basing on the rule of morphologies controlling during electrospinning, we further fabricated nanowire-in-nanotubes via Kirkendall effect. In addition, we fabricated Pt-functionalized NiO nanotubes for performance enhanced gas sensor and carbon nanofibres incorporated with Co3O4nanoparticles for high performance electrochemical energy storage device by electrospinning method. The research achievements in this dissertation can be concluded as below:1. Solvent effect on the morphology of electrospun nanofibres. We have demonstrated that the solvent plays a critical role in the nanotubes formation process which can be controlled by selecting solvent species or adjusting the ambient temperature. It is believed that the rate of evaporation of the solvent during the electrospinning process is the major factors controlling the formation of different electrospun nanofibre morphologies. By their very nature, electrospun different nanofibre morphologies depend on the competition between the phase separation dynamics and the evaporation rate of solvent controlled by the phase diagram of the polymer solution. In our experiments, solid nanofibres and hollow nanofibres are prepared by using different solvent mixtures at a specific ambient temperature (ethanol at room temperature and deionized water homogeneous temperature field of45℃) by single capillary electrospinning process, and compared with solid nanofibers obtained using deionized water at room temperature.2. Wire-in-tube structure fabricated by electrospinning via nanoscale Kirkendall effect. Wire-in-tube structures have previously been prepared using an electrospinning method by means of tuning hydrolysis/alcoholysis of a precursor solution. Nickel-zinc ferrite (Nio sZno sFe2O4) nanowire-in-nanotubes have been prepared as a demonstration. The detailed nanoscale characterization, formation process and magnetic properties of Ni0.5Zn0.5Fe2O4nanowire-in-nanotubes has been studied comprehensively. The average diameters of the outer tubes and inner wires of Ni0.5Zn0.5Fe2O4nanowire-in-nanotubes are around120nm and42nm, respectively. Each fully calcined individual nanowire-in-nanotube, either the outer-tube or the inner-wire, is composed of Ni0.5Zn0.5Fe2O4monocrystallites stacked along the longitudinal direction with random orientation. The process of calcining electrospun polymer composite nanofibres can be viewed as a morphologically template nucleation and precursor diffusion process. This allows the nitrates precursor to diffuse toward the surface of the nanofibres while the oxides (decomposed from hydroxides and nitrates) products diffuse to the core region of the nanofibres:the amorphous nanofibres transforming thereby into crystalline nanowire-in-nanotubes. In addition, the magnetic properties of the Ni0.5Zn0.5Fe2O4nanowire-in-nanotubes were also examined. It is believed that this nanowire-in-nanotube (sometimes called core-shell) structure, with its uniform size and well-controlled orientation of the long nanowire-in-nanotubes, is particularly attractive for use in the field of nano-fluidic devices and nano-energy harvesting devices3. Enhanced gas sensing performance of electrospun Pt-functionalized NiO nanotubes with chemical and electronic sensitization. Pt-functionalized NiO composite nanotubes were synthesized by a simple electrospinning method, and their morphology, chemistry, and crystal structure have been characterized at the nanoscale. It was found that the Pt nanoparticles were dispersed uniformly in the NiO nanotubes, and the Pt-functionalized NiO composite nanotubes showed some dendritic structure in the body of nanotubes just like thorns growing in the nanotubes. Compared with the pristine NiO nanotube based gas sensor and other NiO-based gas sensors reported previously, the Pt-functionalized NiO composite nanotube based gas sensor showed substantially enhanced electrical responses to target gas (methane, hydrogen, acetone, and ethanol), especially ethanol. The NiO-Pt0.7%composite nanotube based gas sensor displayed a response value of20.85at100ppm at ethanol and200℃, whereas the pristine NiO nanotube based gas sensor only showed a response of2.06under the same conditions. Moreover, the Pt-functionalized NiO composite nanotube based gas sensor demonstrated outstanding gas selectivity for ethanol against methane, hydrogen, and acetone. The reason for which the Pt-functionalized NiO composite nanotube based gas sensor obviously enhanced the gas sensing performance is attributed to the role of Pt on the chemical sensitization (catalytic oxidation) of target gases and the electronic sensitization (Fermi-level shifting) of NiO.4. Electrospun carbon nanofibres incorporated with Co3O4nanoparticles as self-supported electrodes for electrochemical capacitors. Flexible porous films are prepared from electrospun carbon nanofibres embedded with Co3O4nanoparticles and are directly applied as self-supported electrodes for high-performance electrochemical capacitors. Uniform Co3O4nanoparticles are well dispersed and embedded into each carbon nanofibres with desirable electrical conductivity. These Co3O4nanoparticles incorporated carbon nanofibres inter-cross each other and formed three-dimensional hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder-free carbon nanofibres/Co3O4nanoparticles hybrid film electrodes exhibit relative high electrochemical performance.