Conducting polymer electrospun nanofibers

Conducting Polymer Electrospun Nanofibers for Chem-/Bio-Sensing... 

The sheet conductivities of the PPy-PEO composite nanofiber mats were in the order of 10" S/cm calculated from the four-probe measurement data. Conductivities of electrospun nanofibers measured by using the four-probe method were about 10" S/cm. PPy was coated on PS nanofiber mats, and the conductivities of the PS-Cl-PPy and PS-TS-PPy fiber mats were found to be 2 x 10" S/ cm and 5 x 10 S/cm, respectively. It was demonstrated that the conductivity of the porous fiber mat could be influenced by the amount (PPy/PS ratio), doping, and crystallinity (polymer chain packing) of PPy in the fibers, the void volume, and the connectivity between fibers in the mat. When the PS template of the PS-TS-PPy fiber mat was removed by THF treatment and the electrical conductivity of the remaining material (TS-PPy) was measured, the conductivity increased to 0.13 S/cm by using the four-probe Van der Pauw method. ... 

At present a few studies of nanofibers and nanombes are focused on CNS drug delivery. One study evaluated electrospun nanofibers of a degradable polymer, PLGA, loaded with antiinflammatory agent, dexamethasone, for neural prosthetic applications (Abidian and Martin, 2005). A conducting polymer, poly(3,4-ethylenedioxythiophene), was deposited to the nano-fiber surface and the coated nanofibers were then mounted on the microfabricated neural microelectrodes, which were implanted into brain. The drug was released by electrical stimulation that induced a local dilation of the coat and increased permeability. 

The last method to be discussed, which is used to form polymer/ceramic composites by electrospinning, is extremely different to the methods previously described, but worth mentioning. Zuo et al. [129] used a method to create a composite scaffold that is actually the reverse of what most people are doing. Instead of mineralizing the nanofibers, Zuo et al. actually incorporated electrospun polymer nanofibers into a ceramic bone cement in order to form a composite scaffold. It was found that by incorporating electrospun nanofibers into the cement, the scaffold became less brittle and actually behaved similarly to that of a ductile material because of the fibers. Composite scaffolds with different polymers and fiber diameters were then tested in order to determine which scaffold demonstrated the most ideal mechanical properties. However, no cell studies were conducted and this method would most likely be used for a bone substitute instead of for bone regeneration applications. 

Other studies in 2000 by Drew et al. reported that it is very difficult to spin fibers of PANI complexed to sulfonated polystyrene (PANFSPS), even when solutions containing sodium chloride and dodecyl benzene sulfonic acid sodium salt were used to lower the surface tension and thereby enhance electrospinning [16,17]. However, PANFSPS nanofibers can be produced by adding a carrier polymer such as PEO, polyacrylonitrile, or polyurethane. Also reported was the use of electrostatically layered sulfonated polystyrene as a template for the surface polymerization of conjugated polymers in their conducting form. Enzymatic synthesis of PANI and a copolymer of pyrrole and PEDOT was done on electrospun nanofiber... 

Figure 4.10 SEM micrographs of electrospun nanofibers from (a) aqueous solutions of 1.5 wt% PEO as carrier with PPy content of 71.5 wt%, (b) 7.5wt% [(PPy3) (DEHS) ]x solution in DMF. The scale bar is Igm. (Reprinted with permission from Polymer, Conductive polypyrrole nanofibers via electrospinning Electrical and morphological properties by I. S. Chronakis, S. Grapenson and A. Jakob, 47, 1597-1603. Copyright (2006) Elsevier Ltd)...

Electrospun Nanofibers from Other Conductive Polymers... 

Electrospun nanofibers with electrical and electro-optical activities have received a great deal of interest in recent years because of their potential applications in nanoscale electronic and optoelectronic devices, for example nanowires, LEDs, photocells etc. Besides, one-dimensional (1-D) nanostmctures are the smallest dimensional stmctures for efficient transport of electrons and optical excitations. One of the potential future apphcations of conducting polymer nanofibers is as molecular wires, which are required to connect molecular devices to electrodes. For molecular devices, it is necessary to make nanowires with diameters in the order of the size of the molecular device. 

M. Kotaki, X-M. Liu, and C. He, Optical properties of electrospun nanofibers of conducting polymer-based blends, J. Nanosci. NanotechnoL, 6, 3997-4000 (2006). 

Some authors have proposed several modified process approaches to obtain electroactive electrospun nanofibers. One first practical and easy way is to spin a nonconductive polymeric web and after polymerize conductive polymers onto the fiber surface. For example, conductive polyamide-6 (PA-6] nanofibers were prepared by polymerizing pyrrole (Py] molecules directly on the fiber surface of PA-6. First, a solution of PA-6 added with ferric chloride in formic acid was electrospun with average diameter values around 260 nm. 

Electrospun conducting polymer nanofibers (diameter ca. 120 nm) also exhibited a desirable electrochromic property [438]. The electrospun conducting polymer nanofibers formed an interconnected network by solid/ swollen-state oxidative crosslinking without significant perturbation of the morphology. Nanofibers showed relatively fast switching times of 2-3 s. 

Although the potential applications of electrospun polymer/CNT nanofibers have yet to be fully exploited, conducting electrospun polymer/CNT nanofibers have been demonstrated to be attractive for a large variety of potential applications, including in optoelectronic and sensing devices (43). Owing to the... 

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