Electrospinning techniques

Li et al. reported pyrochlore-structured La2Zr2Q7 prepared by electrospinning technique from PVP/lanthanum nitrate/zirconium oxychloride as precursors, which was then calcinated at 1000 °C for 12 h, with a diameter of 100-500 run (Figure 56) (Li et al., 2006b). The fiber structure shows a low sintering ability, which could be attributed to the random stacking of fiber, resulting in a structure with low contact area between fibers. 

Another limitation that is specific to the parallel plate electrospinning technique is the collection of extremely thin nanofibers, which have been observed to break because they were unable to sustain the forces of their own weight and of the repulsive charges from other fibers [62]. An electrically resistive substrate inserted into the gap between the plates can provide support to fibers suspended between the plates without influencing fiber quality [62], and may also help to shield any conductive materials below the air gap, which may attract unwanted non-aligned nanofibers. Substrates with bulk resistivity greater than 10 Q cm, such as quartz and polystyrene, are suitable for placement between parallel electrodes, while materials with bulk resistivity of less than 10 Q cm, such as glass, may result in random fiber orientations [67, 68]. 

Kidoaki S. Kwon IK, Matsuda T (2005) Mesoscopic spatial designs of nano- and microflber meshes for tissue-engineering matrix and scaffold based on newly devised multilayering and mixing electrospinning techniques. Biomaterials 26( 1 ) 37-46... 

Despite the fact that the electrospinning technique is relatively easy to use, there are a number of process parameters that can greatly affect fiber formation and structure. Listed in order of relative impact to the electrospinning process, the most important parameters are applied voltage, polymer flow rate, and capillary-collector distance. All three parameters can influence the formation of nanofibers with bead-like defects. 

Polymer-supported Ag nanoparticles have been widely investigated and provide potential applications as catalysts, photonic and electronic sensors, wound dressings, body wall repairs, augmentation devices, tissue scaffolds, and antimicrobial filters [15-22]. For these applications, Ag nanoparticles have to be supported in a biocompatible polymer system [23-26]. The electrospinning technique has often been adopted for the incorporation of Ag nanoparticles into polymer porous media. In this chapter, we review the preparation methods and properties of Ag nanoparticles incorporated into polymeric nanofibers and their applications in the fields of filtration, catalysis, tissue engineering and wound dressing. 

The seventh trend is the increasing use of novel processing methods. For example, there is growing use of supercritical fluids (e.g., supercritical carbon dioxide and nitrogen gases) to foam polyolefin blends for density reduction. There is use of ultrasound to, for example, devulcanize cross-linked rubber. There is use of solid-state shear mechanical processing to break the polyolefin blend material into submicron particles to make environment friendly (water-based) polyolefin dispersions. There is use of electrospinning technique to make polyolefin fibers and in particular nanofibers. 

Electrospinning techniques enable the production of continuous fibers with dimensions on the scale of nanometers from a wide range of natural and synthetic polymers [135]. The number of recent studies regarding electrospun polysaccharides and their derivatives, which are potentially useful for regenerative medicine, is dramatically increasing. 

Dai H, Gong J, Kim H, Lee D. A novel method for preparing ultra-fine alumina-borate oxide fibres via an electrospinning technique. Nanotechnology 2002 13 674-677. 

Guan H, Shao C, Wen S, Chen B, Gong J, Yang X. Preparation and characterization of NiO nanofibres via an electrospinning technique. Mater. Chem. Phys. 2003 6 1302-1303. 

Extremely low-dimensional conducting nanowires (as small as 3 nm in diameter) for use in nanoelectronics can be produced with the electrospinning technique [103]. Using template methods, insulating PLA fibers with an average diameter of 200-700 nm as core materials were electrospun and subsequently coated with thin 50-100 nm films of polyaniline or polypyrrole by in situ polymer deposition methods. The PLA core fibers decompose upon relatively mild thermal treatment under inert atmosphere, leaving... 

Models have been constructed with cross-sections that have diameters of 7-8 nm. They are comparable in thickness with some of the nanofibers prepared by the electrospinning technique, which can be as thin as 3 nm (D. H. Reneker, personal communication). If the fiber has a thickness greater than about 4 nm, it recovers bulk density in its interior. 

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