Effects Of Electric Field Distribution On Molecular Orientation And Crystallinity In Electrospun Polyethylene Oxide Nanofibers

Electrospinning is a technology that a polymer solution is stretched forming ultrafine fibers in the role of high voltage electric field through a very short period of time. Electrospun fibers obtained finer fiber than traditional spinning, with a small diameter, high surface area, high adsorption characteristics. They are widely used in the composite nanofiber material, filtration, separation membranes, biomedical applications(including tissue engineering, artificial organs, controlled drug delivery, wound dressings) and protective clothing as well as fuel cells and other fields. However, poor mechanical properties of electrospun fibers limit its application area. Molecular orientation and crystallinity of electrospun fibers are important factors affecting mechanical properties of fibers. In this thesis, the effects of some parameters on orientation and crystallinity of electrospun fibers are studied.To explore the effect of the electric field distribution on fiber orientation and crystallinity, we change the spinneret structure to achieve the purpose of changing the electric field distribution of the electrospinning. In the second chapter, we use a single hole electrospinning apparatus and conduct the contradistinctive experiments with conventional needle electrospinning apparatus under different rotary speeds of the collector, flow rates, spinning distances and spinning voltages. The molecular orientation of the collected fibers is measured by Fourier transform infrared spectroscopy(FTIR). Crystallinity of the fibers is measured with X-ray diffraction(XRD). Comsol software is simultaneously used to simulate the electric field distribution of the electrospinning devices.Experimental results show that fibers obtained by needle electrospinning apparatus have better orientation than those that obtained by flat hole electrospinning apparatus, and orientation distribution in fibers obtained by flat hole electrostatic spinning apparatus is narrower along a process parameters change. In a certain range, with increasing spinning voltage, spinning flow and spinning distance, the molecular orientation in fibers obtained by the two spinnerets show the trend first increasing and then decreasing. Simulation results show that the distribution of external electric field of nozzle hole is more uniform, and the average electric field strength of spinning area is stronger. Simulation results show that the electric field strength in the needle tip area of the needle spinneret is stronger than that of the corresponding position of the hole spinneret. The simulation results give the explanation for the experimental results.In the third chapter, we explore the effects of the processing parameters, including rotational speed, spinning voltage, spinning flow, spinning distance, on the crystallinity of electrospun fibers. Experimental results show that the trends for orientation and crystallinity under different processing parameters are similar, indicating the relevance of the orientation and crystallinity of the fibers.In Chapter IV, to explore the effect of collector on the electric field distribution and subsequently the molecular orientation of the electrospun fibers, parallel plate electrodes and the roller device are used as collectors for contradistinctive experiments. Experimental results show that fibers obtained by parallel plate electrodes have better orientation than those that obtained by roller device. In a certain range, with increasing spinning voltage, spinning flow and spinning distance, the molecular orientation in fibers obtained by the two collectors show the trend first increasing and then decreasing. Simulation results the electric field strength between the parallel plate electrodes is stronger than that of the corresponding position of the roller device. The simulation results give the explanation for the experimental results.