The Electrospinning Technique

Cloupeau and Prunet-Foch [4] described the different modes of jets that can arise when a potential difference is applied to the tip of a capillary containing a liquid. The different modes depend on geometric factors (such as the distance between the needle and the screen), the flow of the material properties of the liquid (such as surface tension and electrical conductivity) and the applied potential. 

In the drop form there is no electric field effect and the liquid flows drop by drop. Increasing the potential from zero starts the so-called micro dripping. There is an increase in speed and a reduction drip drop size. This behavior has two main causes the liquid is attracted to the grounded collector due to the action of the external elecfiic field and the surface tension is reduced due to the accumulation of charges on the surface of the pendent drop [4, 5]. 

Kopp Alves et al., Novel Synthesis and Characterization of Nanostructured Materials, Engineering Materials, DOl 10.1007/978-3-642-41275-2 4, 

At larger potentials the Taylor cone starts to form. The drop is deformed by the electric field and takes the form of a cone [4, 5], If the potential is slightly lower than the potential to form a continuous stream, a flashing cone is 

With even greater potentials, the cone becomes unstable and more jets emerge from the surface of the liquid it is the start of the so-called multi-jet. The number of jets increases with the increase of the potential. Ramifications may occur due to the high amount of electrical charges in the unstable fluid [4, 5]. The jet does not have a uniform thickness and one or more jets emerge from the surface of the fluid being emitted in various directions. 

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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. 

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. 

In the electrospinning technique, the ejected charged jet was affected by electrical forces, so it is needed to have high electrical properties, i.e., a good dielectric constant, to enhance the density of charges at the surface of the jet for better stretching and uniform formation of fibers with bead-free morphology, ... 

Antibacterial membranes with a multicomponent system containing Ag, AgBr, Ti02, and hydroxyapatite as four active components were used to obtain more efficient antibacterial activity. Additionally polyurethane nanofiber webs containing silver nanoparticles using the electrospinning technique were obtained with the stability of nanoparticles after washing cycles... 

Charernsriwilaiwat, N., Opanasopit, P., Rojanarata, T., Ngawhirunpat, T. and Supaphol, P. 2010. Preparation and characterization of chitosan-hydroxybenzotriazole/polyvinyl alcohol blend nano fibers by the electrospinning technique. 81 ... 

Electrospinning techniques are used to form particles and fibers as small as one nanometer in a principal direction. The phenomenon of electrospray involves the formation of a droplet of polymer melt at an end of a needle, the electric charging of that droplet, and an expulsion of parts of the droplet because of the repulsive electric force due to the electric charges. In electrospraying, a solvent present in the parts of the droplet evaporates and small particles are formed but not fibers. The electrospinning technique is similar to the electrospray technique. However, in electrospinning and during the expulsion, fibers are formed from the liquid as the parts are expelled (41). 

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