Analysis And Verification On Influencing Factors Of Nanofiber Morphology By Electrospinning

Electrospinning technique is the main method of preparing polymer nanofiber simply, directly and continuously. It originates from electrically charged fluid formed jets in the high voltage electrostatic field. Its study involves a variety of disciplines, including rheology, electrostatic field, and instantaneity of its process. So its theory is little researched between parameters and nanofiber diameter.Firstly, electric potential and the moving jet subjected to the applied force were introduced systematically in electrostatic field. Solution viscosity and electrical conductivity affected two significant parameters on fiber diameter in the electrospinning process. Based on theoretical analysis of voltage and the jet radius did by former researchers. At surface charge from part to full on the polymer jet cases, the theoretical analysis proves the effect of solution viscosity on fiber diameter in this paper, that is to say, there has a direct proportion relationship among the fiber diameter, viscosity and surface charge on the polymer jet.Poly(ethylene oxide)(PEO)/wate,poly (amic acid) (PAA)/N, N-Dimethylace-tamide (DMAc) solutions and multi-walled carbon nanotubes/poly(mphenylene isophtalamide) (MWNTs/PMIA/DMAc) blend solution were spun by homemade electrospinning setup. Three different polymer nanofibers were used to verify the direct proportion relationship.PEO was dissolved in water to form four different solution concentrations when molecular weight was 4×105. In order to find optimal salt content, different inorganic salt contents were added in these solutions. Electrical conductivity was tested by the digital conductivity meter with a conductivity electrode, we found that electrical conductivity was dramatically increased when 0.2wt% salt content changed to 0.3wt%, but electrical conductivity hardly changed when 0.4wt% salt content changed to 0.5wt%. We also found that the fibers appeared a connective filament phenomenon between the needle tip and collector plane when LiCl was above 0.3wt%. So 0.2wt% and 0.3wt% were optimal salt contents of experimental verification.Different solutions were electrospun with 0.2wt% and 0.3wt% LiCl contents. The morphology of samples was observed using scanning electron microscopy(SEM). The diameters of electrospun nanofibers were obtained by measuring SEM images using Image Pro-plus 6.0. We found that average diameter and the dispersion of fiber diameter were relatively reduced with increasing salt content. However, fiber diameter hardly changed with increasing solution viscosity. So solution viscosity affected fiber diameter size more important than electrical conductivity. The electrospinning process became stable and easy by adding salt. The fibers had a regular and cylindrical morphology, and a bimodal distribution of fiber diameter disappeared.Verification of PEO nanofibers incidated experimental data agreed well with our theoretical prediction.PAA solution of 40wt% was synthesized by a well-developed procedure using equal molar ratio of 4,4'-oxydiphthalic acid (ODPA) and p-phenylenediamine (PPD) in N,N-Dimethylacetamide (DMAc) under nitrogen purge at 40℃, and then synthesis solution was diluted to 22wt%,24wt%,26wt% and 28wt% using DMAc. The four percentages were added with 0.1 wt%,0.2wt%,0.3wt%,0.4wt% and 0.5wt% LiCl at room temperature, respectively. Using the same test method as chapter 3, choosing optimal salt content was 0.2wt% and 0.4wt%.Different solutions were electrospun when LiCl contents were 0.2wt% and 0.4wt%. Using the same test method with PEO, we found the morphology and diameter of electrospun PAA nanofibers had the same change law as PEO.By analyzing PAA nanofibers, we found that the experimental data slightly deviated from our prediction when the content of salt was less, but the experimental data agreed quite well with theoretical relationship with increasing the content of salt. Blend solutions (MWNTs/PMIA= Owt%, 1wt%,1.5wt% and 2wt%, PMIA=12.5wt%) were prepared using in-situ polymerization and blend solution (MWNTs/PMIA=1wt%, PMIA=12.5wt%) was diluted to 9wt%,10wt% and 11wt%, and then these solution were spun.Electrical conductivity and the electrospun fiber morphology were analyzed when DMAc contents were different. We found that electrical conductivity had been increased when DMAc contents increased. And the fibers had a uniformly average diameter, formation of spindle like and fiber diameter were relatively increased with decreasing DMAc contents.Electrical conductivity and the morphology of electrospun fiber were analyzed when MWNTs contents were different. We found that electrical conductivity had been dramatically increased with increasing MWNTs content. The fibers had a small and uniformly average diameter, and the dispersion of fiber diameter was relatively reduced with increasing MWNTs contents. But the fibers could appear seriously doubling phenomenon because of its high viscosity with improving MWNTs contents.In order to study thermal stability property and crystal properties of composite nanofibers, MWNTs/PMIA and PMIA nanofibers were tested using thermal gravimetric analyzer (TGA) and X-ray diffraction (XRD). TGA data indicated that the onset decomposition temperatures of MWNTs/PMIA composite nanofibers were not obviously enhanced than that of PMIA nanofibers, but thermal stability property was improved with increasing MWNTs content. Added MWNTs could result in larger grain size and higher crystallinity but it could not change PMIA crystal structure.Transmission electron microscopy (TEM) of PMIA composite and pure nanofibers revealed the distribution of MWNTs within the PMIA matrix. MWNTs were aligned along the axis of PMIA composite nanofibers. Most of MWNTs were aggregated in the centered nanofiber because the electrostatic force effect of the cone-jet, resulting in form similarly coaxial composite nanofibers, this phenomenon became more obvious with increasing MWNTs content. Compared with the pure PMIA nanofibers, the composite nanofibers exhibited relatively rough surfaces with increasing MWNTs content. Experimental verification of composite nanofibers (MWNTs/PMIA=1wt%) incidated that our experimental data agreed quite well with our theoretical prediction when PMIA concentration was 12.5wt%.