Preparation And Properties Of Electrospun Well-aligned Nanofibers

Because of unique photonic properties, electrical properties and magnetic properties et al., well-aligned nanofibers are potentially of great technological interest for the development of electronic, biology, medicine, clothes), and others. Electrospinning technology has been recognized as one of the most convenient, direct and economical methods for the fabrication of polymer nanofibers. But the charged jet is instable during the electrospinning process, which leads to the uneven construction of nano-fibers and bad sequent. It is desirable to develop an approach that is able to generate well-aligned nanofibers. For example, the alignment of fibers can improve mechanical properties of fiber composites. In the fabrication of electronic and photonic devices, well-aligned and highly ordered architectures are often required. And well-ordered fibers may also be suitable for many applications in tissue engineering. Therefore, controllable fabrication of well-aligned nanofibers by electrospinning has become a hot subject in the world.In this paper, the advantages of parallel electrode method and additional ring electrode method were combined to design a modified parallel electrodes method by placing a positively charged ring between the needle and the parallel electrodes collector to improve the degree of alignment of electrospun nanofibers. The thesis studied the mechanism of preparing well-aligned nanofibers to optimize electrospinning device and obtain the optimal spinning parameters. The electrospun well-aligned nanofibers were prepared by controlling electrospinning parameters. And the properties of obtained nanofiber mats were investigated to provide the experimental and theoretical basis for the formation mechanism of the well-aligned electrospun nanofibers.Firstly, a positively charged ring was placed between the needle and the parallel electrodes collector in the electrospinning process to control the instability of jet. The results showed the swing scope with a ring is smaller than that without a ring, and the ring could decrease the diameter of nanofibers and enhance the uniformity of diameter distribution.In addition, the electrospun well-aligned nanofibers were prepared by adjusting electrospinning parameters to explore optimal electrospinning parameters. The results showed when the concentration of PAN solution was 10%, the ring voltage was 5kv, the applied spinning voltage was 15 kv and the total distance from the tip of the syringe to the collector was 15 cm, the well-aligned nanofibers with smooth surface could be easily obtained.Then, the influence of hot-drawing treatments was researched on the degree of alignment, exothermic peak, crystallization and mechanical properties of composite nanofibers. The results showed the heat treatment could make the arrangement of nanofibers become denser, decrease the amount of entangled nanofibers and improve the degree of alignment of nanofibers. And the crystallinity of the hot-stretched fibrous membranes confirmed by X-ray diffraction analysis enhanced obviously. The exothermic peak temperature of the hot-stretched membranes confirmed by Differential Scanning Calorimetry decreased obviously. That meant the crystalline microstructure of the PAN nanofibers after hot-drawing treatment developed well, and the improved nanofiber alignment and crystallinity resulted in the increased tensile strength of the nanofibrous membranes.Finally, the effects of additives(Na Cl and MWCNTs) on the diameter, alignment degree, and mechanical properties of composite nanofibers were researched. When additives were added the well-aligned nanofibers could be still obtained. However, it would affect the surface morphology and properties of nanofibers obtained. Na Cl additive could improve the conductive of PAN solution. When the content of Na Cl is 5%, Na Cl could disperse homogenously in the solution. With the content of Na Cl increasing, the diameters of Na Cl/PAN nanofibers increased firstly and then decreased, and the breaking strength and elongation of nanofibers showed a trend of decline. Moreover, multiwalled carbon nanotubes(MWCNTs) additive could reunite easily in the solution. With the content of MWCNTs increasing, the surface of nanofibers became coarsening, the diameters of MWCNTs/PAN nanofibers increased, the breaking strength of nanofibers increased firstly and then decreased, and the elongation of nanofibers decreased. When the content of MWCNTs is 1.5%, the breaking strength of MWCNTs/PAN nanofibers reached the maximum value.